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1             UNIVERSITY  OF  ILLINOIS 
S                                  LIBRARY 

1 

•         Class                               Book                           Volume 

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The  person  charging  this  material  is  re- 
sponsible for  its  return  to  the  Hbrary  from 
which  it  was  withdrawn  on  or  before  the 
Latest  Date  stamped  below. 

Theft,  mutilation,  and  underlining  of  books 
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result  in  dismissal  from  the  University. 

UNIVERSITY    OF     ILLINOIS     LIBRARY    AT    URBANA-CHAMPAIGN 


(y     0-      M 


Of  THE 


^\      /  UBRARy 


Hsiry  t/  JLUHOis. 


UNIVERSITY  OF  ILLINOIS  BULLETIN 

Vol  4.  JUN^K  15,  1907  Xo.  23 

[Entered  February  14, 1902,  at  Urbana,  111.,  as  second-class  matter 
under  Act  of  Congress  of  .Tuly  Irt,  1894. 


BUfctETIN^o.^  DEPARTMENT  OF  CERAMICS 

C.  W.  ROLFE,  Director 


Effect  of  Repeated  Freezing  and  Thawing  on 

Brick  Burned  to  Different  Degrees 

of  Hardness 


By  J.  C.  JONES,  B.  S. 


J  906-  \ 907 


PUBLISHED    FORTNIGHTLY   BY   THE   UNIVERSITY 


[Reprinted  from  t)ie  Transactions  of  The  American  Ceramic  Society,  Vol.  tX.     Paper 
read  at  St.  Louis  meeting,  February,  1907.] 


THE  RELATION  OF  HARDNESS  OF  BRICK  TO  THEIR 
RESISTANCE  TO  FROST. 

BY 

J.  C.  Jones,  Champaign,  111. 

OUTLINE. 
Introduction. 

Structure  of  brick. 

Shape  and  size  of  the  clay  grains. 

Pores  and  laminations. 

Origin. 

Relations. 

Effect  of  method  of  manufacture.' 
Changes  in  pore  space  during  burning. 

Period  of  dehydration  and  oxidation. 

Period  of  fusion. 
.  Changes  in  strength  and  rigidity  during  burning. 
Tensile  vs.  compressive  strength. 
Special  case  of  the  salmon  brick. 
Disintegrating  forces  due  to  change  in  temperature. 
Inherent  in  the  brick. 

Unequal  expansion  of  mass. 

Unequal  expansion  of  constituent  parts. 
Factors  foreign  to  brick. 

Must  be  fluid  to  enter  brick. 

Must  become  solid  within  brick. 

Must  be   universally    abundant,    and    solidify   at   ordinary 

temperatures. 

Water  and   salts  dissolved  in  it  are  the  only  substances 

that  fulfill  the  above  conditions. 
Physical  properties  of  water. 

Change  of  volume  with  change  of  temperature. 
Change  of  volume  with  freezing. 
Disintegrating  eifects  of  freezing  water. 
Conditions  preventing  damage. 

Overcooling  of  the  water. 

Imperfect  sealing  of  the  pores. 

Partial  drainage  of  the  pores. 
Laws  governing  the  flow  of  water  through  the  pores. 
Effect  of  laminations. 
Relative  contraction  of  ice  and  brick. 

3 


4  HARDNESS   OF    BRICK  AND   THEIR   RESISTANCE  TO    FKOST. 

Conditions  governing  the  durability  of  the  brick  in  the  wall. 
Foundation. 

Zone  below  the  water  level. 

Zone  of  capillary  action  just  above  the  water  level. 
Wall  a'bove  the  foundation. 
Freezing  tests. 

Methods  of  determining  pore  space. 

By  soaking;   complete  immersion,  partial  immersion. 
By  use  of  air  pump. 
By  boiling. 
Calculation  of  porespace. 
Measurement  of  the  rate  of  absorption. 
Freezing. 
Results  of  a  freezing  test  of  three  series  of  brick. 
Summary  and  conclusion. 

INTRODUCTION. 

It  has  long  been  supposed  that  the  harder  a  brick  is 
burned,  the  greater  will  be  its  resistance  to  frost.  This  is 
based  upon  the  known  fact  that  with  increased  hardness 
of  burning,  there  is  an  increase  in  strength  and  decrease  of 
pore  space.  In  making  freezing  tests,  this  supposition  has 
not  always  been  found  to  be  true.  The  crushing  strength 
has  often  been  found  to  be  most  affected  by  freezing,  in  the 
hardest  burned  brick.  In  order  to  determine,  if  possible, 
the  relations  that  existed  between  the  hardness  of  a  brick 
and  its  resistance  to  frost,  the  present  investigation  was 
undertaken. 

Three  series  of  brick  were  selected,  each  series  contain- 
ing four  different  grades  of  hardness,  and  the  usual  freez- 
ing tests  were  applied.  As  the  investigation  progressed, 
an  analysis  of  the  conditions  to  which  the  bricks  were  sub- 
jected in  the  tests  and  in  the  wall  was  begun.  This  soon 
led  to  new  ideas  concerning  the  factors  involved.  Certain 
additional  experiments  were  therefore  made  to  prove  or 
illustrate  these.  Because  of  the  lack  of  definite  knowledge 
of  the  many  principles  involved,  the  discussion  is  largely 
theoretical,  and  represents  the  belief  of  the  writer.  The 
paper  is  of  a  preliminary  nature,  yet  it  is  believed  it  indi- 
cates the  direction  in  which  the  truth  lies, 


HARDNESS  OF   BRICK   AND  TIIKIi:  ItKSISTANCK  TD    FROST.  5 

The  factors  involvocl  in  tlie  power  of  a  brick  to  resist 
frost  are  the  followiiij*-:  Tlie  structure  of  the  brick,  the 
disintejiratiiiii'  forces,  the  conditions  afPectiiii!,-  the  brick  in 
the  Avail,  and  the  relations  between  these  factors  and  the 
durability  of  the  brick.  A  discussion  of  the  tests  now  in 
use  and  their  value  follows.  Tlie  results  of  the  experiments 
that  brought  the  writer  to  his  conclusions  are  given,  and  ;1 
summary  including  the  tests  believed  to  be  the  most  val- 
uable in  predicting  the  durability  of  brick  closes  the  paper. 

The  writer  wishes  to  acknowledge  the  kindness  of  the 
Def)artments  of  Dairying  and  Applied  Mechanics  of  the 
T^niversitv  of  Illinois  for  the  facilities  placed  at  his  dis- 
posal for  freezing  and  crushing  the  brick  tested.  The  kind- 
ness of  the  manufacturers  who  donated  the  brick,,  of 
Pi'ofessor  C  W.  Rolfe,  who  made  the  investigation  pos- 
sible, of  Professor  R.  A.  Millikan,  of  the  University  of 
Chicago,  and  of  Mr.  Ross  C.  Purdv,  who  aided  the  author 
with  criticism  and  suggestions,  are  also  thankfully  ack- 
tnnvledged. 

STRUCTURE  OF  BRICK. 

.*^7/f//)c  and  fiizr  of  fhr  clnt/  f/raiii.^.  The  clay  from 
which  brick  are  formed  contains  many  minerals.  Among 
those  that  have  been  identified  with  certainty  are  quartz, 
feldspar,  mica,  kaolinite,  iron  oxides,  pyrite,  and  calcite. 
Of  these  kaolinite,  quartz,  feldspar,  and  mica  form  the 
bulk  of  the  clay.  The  grains  of  mica  and  possibly  kaolinite 
originally  had  the  form  of  flattened  plates.  These  have 
been  so  broken  during  the  many  changes  through  Avhich  the 
clay  has  passed  that  their  thickness  often  nearly  equals 
their  length.  The  grains  of  other  minerals  are  approxi- 
mately equal  in  all  dimensions.  With  few  exceptions,  the 
grains  liave  been  worn  and  rounded  by  Aveathering  and 
transportation,  and  it  is  not  far  from  the  truth  to  consider 
them  as  spherical. 

The  following  mechanical  analysis  of  a  clay  similar  to 
that  from  Avhich  one  of  the  sots  of  lu'ick  experimented  upon 
Avas  maniifMrfiiTod,  illust]-af"('-  fl'o  rnivo  io  size  of  the 
grains. 


HARDNESS   OF  BRICK    AXD   THEIR  RESISTANCE  TO    FROST. 


Mechanical  analysis  of  Champaign  subsoil.^ 


Size  of  Grain 

Designation 

Percentage 

2.000-l.OOOmm. 

fine  gravel 

1.04% 

1. 000-0. SOOmm. 

coarse    sand 

1.98% 

.      0.500-0.250mm. 

medium  sand 

6.85% 

0.250-O.lOOmm. 

■    fine  sand 

6.23% 

0.100-0. OoOmm. 

very  fine  sand 

5.82% 

0.050-0.010inm. 

silt 

28.38%, 

O.'OlO-O.OOSmm. 

fine  silt 

15.46% 

0.005-O.OOlmm. 

clay 

30.00% 

Total 


95.76% 


Loss  on  heating,  organic  matter,  water. 


4.24% 


From  this  it  is  seen  that  the  range  in  size  of  grain  is 
considerable,  but  the  most  noticeable  thing  is  the  prepon- 
derance of  the  finest  grains, — which  form  73.84%  of  the 
whole. 

Pores.  Schlichter,-  in  discussing  the  origin  and  rela- 
tions of  pore-space  in  sands  and  sandstone,  has  shown  that 
it  depends  upon  the  size  of  grains,  their  uniformity  of  size, 
and  the  manner  in  which  they  are  packed.  The  larger 
pores  are  produced  by  the  larger  and  more  uniform  grains 
and  the  smaller  ones  by  those  that  are  smaller  and  more 
heterogeneous.  The  maximum  pore-space  with  a  giyen  size 
of  grain  results  when  the  grains  are  arranged  in  a  rectan- 
gular pattern,  the  minimum  when  in  a  triangular  pattern. 
In  eyery  possible  manner  of  packing,  howeyer,  there  is  at 
least  one  direction  in  which  the  interangular  spaces  form 
continuous  tubes. 

On  account  of  the  diyerse  forms  of  the  grains,  these 
tubes  are  not  uniform  throughout  their  length,  but  consist 
of  a  series  of  triangular  cavities  connected  at  their  smaller 
ends.  Owing  to  the  variation  of  the  diameters  of  the 
grains,  these  cavities  are  not  uniform  in  size,  but  are  smal- 
ler or  laroer  as  the  srrains  increase  or  diminish  in  size. 


'Leverett.    U.  S.  Geol.  Surv.,  Monograph  38,  p.  163. 
=Schlichter.     U.  S.  Geol.  Surv.,  19th  Ann.  Rept. 


HARDNESS   OK  BKICK  AND   TIIKIK    RESISTANCE   TO   FKOST.  7 

(."oiiseqiieiitly,  the  pores  have  the  form  of  a  string  of  irregu- 
lar beads  rather  than  that  of  a  continuous  circular  tube. 

Nevertheless,  Schlichter  has  shown  that  these  irregular 
tubes  or  pores  obey  the  same  laws  in  regard  to  the  passage 
of  fluids  through  them  as  do  circular  tubes.  The  internal 
structure  of  unburned  brick  is  that  of  a  more  or  less  closely 
packed  mass  of  sand  and  clay  grains.  Therefore  the  laws 
of  capillary  tubes  may  be  applied  to  such  brick  without 
serious  error. 

JAiminatioihs.  By  whatever  method  brick  are  manu- 
factured, numerous  cracks  and  crevices  arise,  which  are 
relatively  much  larger  in  two  of  their  dimensions  than  in 
the  other.  For  instance,  when  clay  is  forced  through  a 
die,  certain  portions  of  the  column  move  faster  than  the 
rest  and,  slipping  along  definite  planes,  form  fractures  and 
cracks.  The  cracks  formed  b}'  the  blades  of  the  auger  may 
not  heal,  or  they  may  act  as  planes  upon  which  the  clay 
slii)s  as  it  passes  through  the  die.  Air  bubbles  confined  in 
the  clay  are  squeezed  out  flat  and  remain  in  the  brick. 
Whatever  their  origin,  the  cracks  are  of  similar  appearance 
and  are  known  collectively  as  lamination  cracks. 

Lamination  cracks,  in  contrast  to  pores,  are- scattered 
irregularly  through  the  brick,  and  are  but  rarely  in  direct 
contact  with  one  another.  They  are,  however,  connected 
by  the  all-pervading  system  of  pores.  The  pores  and  lami- 
nation cracks  together  make  up  the  total  pore  space  of  the 
brick,  and  their  size  and  abundance  determine  in  an  im- 
portant degree  its  durability. 

Effect  of  method  of  manufacture  and  irater  used  in 
mul'uKj  hrick.  The  manner  in  which  the  grains  of  clay  are 
packed  in  a  brick  is  determined  in  a  large  degree  b,y  the 
method  of  manufacture  and  amount  of  water  used  in  mak- 
ing. In  soft  mud  brick,  for  example,  enough  water  is  added 
to  the  clay  to  form  a  film  around  each  grain.  The  grains 
are  separated  from  each  other  by  this  film,  and  settle  to- 
gether when  the  brick  is  dried.  The  larger  grafns  act  as  a 
sort  of  skeleton  and  prevent  shrinkage  to  a  considerable  ex- 
tent.   The  grains  are,  therefore,  arranged  in  a  i-ather  opeii 


8  HARDNESS  OK    P.IMCK    AM)   '111  KIR   RKSISTAKCK   TO   FROST. 

manner,  and  the  pore  space  approaches  the  maximum 
value  possible  with  the  size  of  grain  present. 

In  the  stiff  mud  brick,  on  the  other  hand,  only  enough 
water  is  added  to  the  clay  to  allow  the  machine  to  handle 
it.  The  clsLj  is  under  heavy  pressure  as  it  pass^  through 
the  die,  and  the  grains  are  crowded  together,  making  the 
brick  compact  and  dense.  When  these  bricks  are  dried, 
there  is  not  the  opportunity  for  the  small  grains  to  settle 
that  was  present  in  soft  mud  brick.  As  a  result,  the  pore 
space  approaches  the  minimum  limit.  The  pores  are  there- 
fore smaller  in  a  stiff -mud  brick  than  in  a  soft-mud  brick 
made  from  the  same  clay.  This  is  illustrated  by  the  shale 
brick  used  in  the  present  tests. 

Effective  diameter  of  pores.  Although  the  pores  are 
far  from  being  -uniform  in  diameter,  yet  it  is.  possible  to 
consider  them  as  being  so.    This  uniform  diameter  would 

be  that  which  would  allow  the  satiie  amount  of  fluid  to  flow 

« 

through  the  pores  when  the  amount  of  pore  space  and  other 
conditions  are  the  same.  This  will  be  spoken  of  hereafter 
as  the  effective  diameter  of  the  pores.  This  term  is  ana- 
logous to  the  effective  diameter  of  grain  defined  by 
Schlichter. 

CHANGES  IN  PORE  SPACE  DURING  THE    BURNING  OF  THE 

BRICK. 

Purdy  and  Moore^  in  a  study  of  the  physical  changes 
that  take  place  during  the  burning  of  brick,  found  that 
porosity  increases  during  the  period  of  dehydration  and 
oxidation,  and  decreases  during  the  period  of  fusion.  One 
of  the  clays  upon  wliich  they  worked,  was  the  shale  from 
which  two  of  the  series  of  brick  used  in  the  present  experi- 
ments were  made.  A  curve,  taken  from  their  results,  shows 
graphically  the  decrease  in  pore  space  during  the  period 
of  fusion.  (See  figure  No.  1,  which  is  the  same  as  Fig. 
XLIX  of  the  Purdy-Moore  series.)  •  ■ 

In  the  same  paper,  is  included  a  microscopic  study  of 


^See  page  204. 


HARDNESS   OF   BRICK  AND   THEIR  RESISTANCE   TO   FROST.  !» 


50 

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TEMPERATURES      EXPRESSED    IN    COMES 


10  HARDNESS   OF   BRICK  XnD  THEIB   RESISTANCE   TO   FROST. 

a  series  of  test  pieces  at  different  stages  of  burning,  made 
by  Wegeman.  His  observations  sliowed  that  witli  tlie 
fusion  of  tlie  material,  the  pore  space  apparently  increased, 
and  took  the  form  of  blebs  or  bubbles  in  the  glass. 

Reasoning  from  known  facts,  the  change  in  pore  space 
that  takes  place  during  the  burning  of  the  brick  is  believed 
to  be  as  follows : 

Period  of  dehydration  and  oxidation.  In  dried  brick, 
the  pores  are  mostly  very  minute  on  account  of  the  fineness 
of  the  grains.  The  salts,  left  from  the  escaped  water,  are 
lodged  most  abundantly  in  the  pores  near  the  surface.  As 
a  result,  these  pores  are  more  or  less  clogged.  During  the 
period  of  dehydration  and  oxidation,  several  of  the  consti- 
tuents of  the  brick  give  off  gases.  Among  these  are:  the 
combined  water,  COo  from  the  carbonates,  and  carbona- 
ceous matter,  SO2  from  the  sulphides  and  sulphates,  etc. 
To  a  certain  extent  the  escaping  gases  act  in  a  manner 
analogous  to  that  of  yeast  in  bread,  and  open  up  and  ex- 
pand the  pores  in  forcing  their  way  out  of  the  brick.  In 
addition,  many  of  the  precipitated  salts  are  volatile  and 
are  removed,  thus  freeing  the  pores.  The  final  result  of 
those  co-operating  factors  is  to  increase  the  pore  space,  by 
opening  the  pores  and  expanding  them.  The  brick,  as  a 
result,  take  up  water  much  more  rapidly  and  abundantly 
than  before. 

Period  of  fusion.  Fusion  begins  with  the  amorphous 
matter  between  the  grains,  causing  them  to  run  together  so 
that  they  lose  their  individuality.  The  pores,  composed  of 
the  spaces  between  the  grains,  begin  to  lose  their  triangu- 
lar form  and  grow  smaller.  Eventually  the  walls  come  in 
contact  at  two  or  more  points  and  portions  of  the  pores 
are  sealed.  The  pores  are  filled  with  gases,  and  when  they 
are  sealed,  these  are  confined,  preventing  further  collapse 
of  the  pores.  As  tlie  glass  becomes  more  fluid,  surface 
tension  causes  the  gaseous  inclusions  to  take  on  a  spherical 
form.  These  minute  bubbles,  as  they  come  in  contact  with 
each  other,  merge  and  form  larger  bubbles.  The  writer 
believes  that  these  last  are  the  blebs,  described  by  Wege- 
mann.  - 


HARDNESS   OF   BRICK  AND   THEIR  RESISTANCE  TO    FROST.  11 

Wlieu  the  pores  are  not  completely  sealed  by  glass, 
they  are  nevertheless  obstructed,  and  their  etfeetive  diame- 
ter decreased.  As  will  be  shown  later,  this  has  an  import- 
ant bearing  upon  the  rapidity  with  which  they  absorb 
water,  and  therefore  upon  the  durability  of  the  brick.  It  is 
probable  that  the  only  decrease  in  actual  pore  space  comes 
about  through  shrinkage  of  the  brick,  and  collapse  of  the 
unsealed  pores.  Much  of  the  apparent  decrease  is  due  to 
the  sealing  of  portions  of  pores  by  glass,  and  consequent 
isolation  of  these  parts  from  the  all-pervading  system  of 
pores  that  existed  in  the  unfused  brick.  The  pore  space 
is  commonly  measured  by  the  amount  of  water  a  brick 
can  absorb,  and  only  that  portion  of  the  total  pore  space 
is  included  which  offers  a  free  passage  to  water.  This 
leaves  out  of  consideration  the  minute  and  sealed  pores, 
and  the  apparent  decrease  in  a  large  measure  represents 
these. 

The  changes,  then,  that  take  place  in  pore  space  dur- 
ing burning  are:  First,  the  enlargement  and  clearing  of 
the  pores  during  the  period  of  dehydration  and  oxidation 
resulting  from  the  volatilization  of  the  obstructing  salts 
and  the  mechanical  effect  of  the  escaping  gases;  second, 
the  obstruction  of  the  pores  by  glass  formed  during  the 
period  of  fusion,  and  the  partial  or  complete  isolation  of 
the  pores  included  in  the  fused  portions  of  the  brick. 

CHANGES  IN  STRENGTH  AND  RIGIDITY  DURING  BURNING. 

As  brick  are  burned,  they  gain  in  strength,  as  has  been 
shown  by  numerous  crushing  tests.  This  is  due  to  the 
better  consolidation  of  the  grains  of  clay,  and  the  more 
perfect  contact  that  is  produced  by  their  partial  fusion 
with  increased  heat  treatment.  The  brick  gains  in  tenac- 
ity, therefore,  and  develops  greater  resistance  to  disinte- 
grating forces  as  burning  progresses. 

Along  with  this  increase  in  strength,  goes  increased 
rigidity  and  consequent  brittleness.  While  it  takes  a 
greater  initial  force  to  start  disruption  in  the  harder 
burned  brick,  the  distance  through  which  the  force  must 


12  HARDNESS   OF   BRICK  AND   THEIR   RESISTANCE   TO   FROST. 

act  in  order  to  cause  complete  failure  is  lessened.  This  is 
caused  by  the  fact  that  liard  brittle  substances  cannot  be 
strained  as  far  without  breaking,  as  the  softer  and  tougher 
materials.  This  has  an  important  bearing  upon  the  resist- 
ance a  brick  offers  to  disintegration  by  frost. 

As  an  illustration,  consider  the  conditions  and  action 
of  a  brick  in  the  wall  of  a  burning  building.  The  sudden 
change  of  temperature  expands  the  surface  of  the  brick 
more  rapidly  than  the  body,  on  account  of  the  slowness 
with  which  the  heat  is  conducted  to  the  interior.  When 
water  is  thrown  upon  the  wall  the  surface  is  cooled  very 
much  more  rapidly  than  the  interior.  The  surface  of  the 
brick  becomes  relatively  smaller  than  the  body,  and  a  stress 
results  between  them.  If  this-  stress  is  great  enough  to 
overcome  the  resisting  strength,  and  the  amount  of  con- 
traction is  enough  to  exceed  the  elastic  limit, — or  the  dis- 
tance which  a  brick  may  be  strained  without  injury — the 
brick  gives  way  and  spalls  off.  If  the  amount  of  contrac- 
tion does  not  exceed  the  elastic  limit,  the  brick  is  not 
injured,  since  the  strained  parts  return  to  their  former 
positions  as  soon  as  the  stress  is  removed.  A  little  brick 
has  a  small  elastic  limit,  and  will  often  fly  to  pieces  under 
conditions  where  a  softer  brick  will  stand.  The  harder 
burned  brick,  therefore,  have  the  greater  initial  strength 
to  resist  strains,  but  give  way  more  rapidly  after  movement 
is  once  started. 

Tensile  strength  versus  compressive  strength.  The 
distance  through  which  the  walls  of  the  pores  are 
forced  by  the  expansion  of  freezing  water  depends  upon 
whether  the  tensile  strength  of  the  brick  is  greater  than  the 
compressive  resistance,  or  vice-versa.  As  an  illustration, 
consider  a  pore  near  the  surface  of  the  brick.  If  the  tensile 
strength  is  the  weaker,  the  material  at  the  surface  will 
give  way  and  spall  off.  As  a  result  the  pore  will  expand  in 
but  one  direction,  i.  e.,  towards  the  surface.  If,  on  the 
other  hand,  the  tensile  strength  is  the  stronger  and  the 
material  holds,  the  pore  will  have  equal  pressure  on  all 
sides  and  expand  in  all  directions. 


HARDNESS   OF   BRICK  AND   THEIR  RESISTANCE  TO   FKOST.  18 

If  tlie  poros  be  considered  as  circular  tubes,  this  fact 
may  be  stated  quantitatively.  Kepresentin<>-  the  radius  of 
the  pore  as  r  and  its  length  as  l^  the  volume  of  the  pore  will 
be  ''Ur-,"  Representino-  the  expansion  of  water  as  "'^a'  the 
total  expansion  of  a  tilled  pore  will  be  "aUr~.'^  If  the 
expansion  takes  place  in  one  direction  only,  as  in  the  first 
case,  tlie  distance  that  part  of  the  wall  must  move  is  equal 
to  the  total  expansion  of  the  confined  water  divided  by  the 
length  of  the  tube,  or  ^^anr^/'  That  is,  the  distance  the 
wall  of  the  pore  is  strained  is  in  this  case  proportional  to 
the  square  of  the  radius. 

If,  as  in  the  second  case,  the  expansion  takes  place  in 
all  directions,  tlie  distance  any  part  of  the  Avails  move  is 
the  total  expansion  divided  by  the  number  of  directions 
of  movement,  or 

alTrr-  ar 


.'iTrr 


That  is,  tlie  distance  the  walls  of  the  pore  are  strained  is 
jtroportional  to  the  radius.  This  indicates  that  the  dis- 
tance any  part  of  the  wall  of  a  pore  moves  in  consequence 
of  the  expansion  of  the  water,  is  much  greater  in  the  first 
case  than  in  the  second.  The  chances  are  much  greater, 
therefore,  that  the  elastic  limit  of  a  brick  will  be  exceeded 
when  it  possesses  greater  rigidity  than  tensile  strength. 

The  actual  expansion  in  a  brick  probably  lies  between 
the  two  values  given,  and  depends  not  only  upon  the  size 
of  the  pores,  but  the  rigidity  of  the  brick  also.  In  the 
softer  l)rick,  which  are  less  rigid,  the  expansion  of  the  walls 
will  be  more  nearly  proportional  to  tlie  radii  of  the  pores. 
In  the  harder  brick,  on  the  other  hand,  in  which  rigidity  is 
greater,  the  ex])ansion  will  be  more  nearly  proportional  to 
the  square  of  tlie  radii.  The  advantage  gained  b}^  the  smal- 
ler pores  of  harder  brick  is  in  a  measure  offset  by  their 
increased. rigidity  and  smaller  elastic  limit. 

Special  case  of  the  salmon  hrick.     Purdy  and  Moore 


14  HARDNESS   OF   BRICK  AND  THEIR   RESISTANCE   TO   FROST. 

have  called  attention  to  the  fact^  that  some  clays  disin- 
tegrate and  slake  when  placed  in  water,  becoming  plastic 
again  even  after  having  been  burned  to  the  temperature  of 
1100  degrees  F  for  many  hours.  They  explain  this  phenom- 
enon as  due  to  the  action  of  adsorbed  salts,  and  it  may  be 
possible  that  this  is  more  common  than  is  at  present  sup- 
l>osed.  If  this  is  true,  the  rapid  weathering  of  some  salmon 
brick  is  easily  explained.  In  all  harder  burned  brick, 
lioweA^er,  this  factor  does  not  enter,  as  the  adsorbed  salts 
are  changed  to  a  harmless  form  at  the  temperature  at 
which  dehydration  and  oxidation  is  finished.  Consequently, 
it  may  be  omitted  in  the  discussion  of  the  brick  burned  be- 
yond this  stage. 

The  changes  that  take  place  in  the  strength  of  brick  dur- 
ing burning  are,  therefore,  increase  in  tenacity,  due  to 
consolidation  and  amalgamation  of  the  clay  grains;  in- 
crease in  rigidity  and  brittleness;  increase  in  durability 
due  to  change  of  adsorbed  salts  to  a  harmless  form.  The 
increase  in  strength  increases  the  initial  strain  the  brick 
can  withstand,  and  the  increase  in  rigidity  decreases  the 
elastic  limit  and,  therefore,  the  distance  the  parts  of  the 
brick  can  be  strained  without  injury, 

DISINTEGRATING  FORCES  DUE  TO  CHANGE  IN 
TEMPERATURE. 

Factors  inherent  in  hrick.  Brick,  which  are  merely 
artificial  stones,  have  many  characteristics  in  common  with 
rocks  and  many  known  facts  concerning  building  stones 
may  be  applied  to  bricks.  Every  geologist  is  familiar  with 
the  immense  amount  of  disintegration  that  rocks  undergo 
from  simple  changes  in  temperature.  This  is  especially 
true  in  situations,  as  on  mountain  slopes,  where  diurnal 
changes  are  rapid.  MerrilP  cites  several  observations  of 
the  effect  of  rapidly  changing  temperature  on  rocks.  He 
tells  of  finding  numerous  fresh  chips  and  flakes  in  the 
valleys  and  on  the  slopes  of  a  mountain  in  Montana,  that 


'See  page  213,  this  volume 

"Rocks,  Rock  Weathering,  and  Soils,  p.  181. 


HARDNESS  OF   BRICK  AND   THKIR  RESISTANCE  TO   FROST.  15 

c-oul(l  only  be  accounted  for  by  the  action  of  rapid  cliange 
in  temperature  during  day  and  night.  Another  observation 
lie  quotes  is  tliat  of  Livingston,  who  reported  that  rocks 
in  Africa  were  frequently  heated  to  a  temperature  of  13 T 
degrees  Fahrenheit  during  the  day,  and  that  rapid  cooling 
during  the  night  split  off  fragments  weighing  as  much  as 
200  pounds.  The  fundamental  cause  of  this  disruption  is 
the  poor  heat  conductivity  of  the  rocks. 

Kocks  and  clay  products  are  poor  conductors  of  heat. 
A  difference  in  temperature  of  100  degrees  may  arise  in  a 
depth  of  one  inch  when  a  rock  is  simply  heated  by  the  rays 
of  the  sun.  The  coefficient  of  expansion  of  rocks  is  approx- 
imately .000005.  In  a  rock  100  feet  long  when  the  above 
conditions  exist,  the  difference  between  the  length  of  its 
heated  surface  and  that  of  a  zoiu^  one  inch  lower  would  be 
nearly  one-half  inch.  This  places  the  rock  under  a  tremen- 
dous strain,  and  since  rocks  are  very  rigid,  the  strain  is 
concentrated  at  the  weak(^st  point.  Eventually  the  strain 
becoiiH^s  greater  than  the  rock  can  bear  and  it  gives  way. 

This  same  principle  operates  on  brick,  and  is  apparent 
in  the  chipped  surfaces  of  a  brick  wall  that  has  ])assed 
through  a  severe  fir(\  Tender  ordinary  circumstances,  the 
greatest  difference  in  tem]»(Mature  exists  between  the  faces 
of  a  wall  heated  to  room  temperature  on  the  inside  and 
cooled  to  the  temperature  of  the  air  on  the  outside.  This 
difference  is  at  a  maximum  during  winter  and  probably 
amounts  to  100  (legi*ees  V.  Since,  however,  the  bricks  are 
separated  from  each  other  by  much  weaker  mortar  joints, 
the  wall  does  not  act  as  a  single  unit,  as  a  rock  mass  does, 
but  as  a  multitude  of  units.  Therefju-e  the  differential  ex- 
pansion oi*  contraction  cannot  be  concentrated  u])on  a 
weak  point  as  it  is  in  rocks,  lnit  is  confined  to  each  brick. 
The  difference  in  length  of  the  outer  and  inner  surfaces 
of  a  brick  under  these  circumstances  is  only  .0025  of  an 
inch.  This  certainly  does  not  exceed  the  elastic  limit  of 
the  brick  and  need  not  be  taken  into  account.  The  same 
process  that  is  so  effective  in  disrupting  the  rocks  is  inef- 
fectual in  l)rick  under  ordinary  conditions,  simply  because 


16  HARDNESS   OF   BRICK   AND   THEIR   RESISTANCE  TO   FROST. 

their  small  size  and  elastic  connections  render  it  impossible 
for  cumulative  strain  to  concentrate  at  any  one  point. 

A  factor  operative  in  the  crystalline  rocks,  especially 
of  the  coarse  grained  granite  type,  is  the  internal  strains 
set  up  by  unequal  expansion  of  the  different  minerals. 
Here(  as  above,  the  amount  of  differential  strain  depends 
directly  upon  the  size  of  the  grains,  increasing  as  the  size 
of  the  grains  increases.  As  most  of  the  material  that  forms^ 
brick  is  very  tine  grained  and  becomes  more  homogeneous 
with  burning,  this  differential  strain  is  too  small  to  have 
any  effect. 

Factors  foreuin  to  the  hriel\  Since  it  has  been  shown 
that  there  is  nothing  inherent  in  brick  that  will 
cause  their  weakening  with  ordinary  temperature  changes, 
the  disrupting  factor  must  be  some  external  substance  that 
may  find  entrance  into  them  and,  by  its  different  rate  of 
expansion,  set  up  strains.  Of  necessity  this  must  be  a  sub- 
stance that  is  fluid  at  least  at  the  time  of  its  entrance  into 
the  brick.  The  conditions  require  that  it  be  mobile  and 
able  to  flow  through  the  pores.  Further,  it  must  have  a 
different  rate  of  expansion  from  that  of  the  brick,  in  order 
that  a  differential  expansion  and  consequent  strain  may 
exist  with  change  of  temperature.  In  order  that  this  may 
be  effective  as  a  disrupting  force,  it  is  further  necessary 
that  the  substance  be  confined  to  a  considerable  degree,  so 
that  the  strains  will  not  be  relieved  by  reverse  flow  of  the 
substance. 

Liquids  and  gases  fulfill  the  first  two  conditions  per- 
fectly, but  as  the  same  properties  that  permit  their  en- 
trance into  the  brick  also  allow  their  escape,  they  cannot 
cause  strain  that  will  mechanically  harm  the  brick  under 
ordinary  conditions.  All  three  conditions  are  only  fulfilled 
by  some  substance  that,  fluid  at  the  time  of  entrance,  be- 
comes rigid  with  change  of  temperature,  or  other  ordinary 
conditions,  and  thus  renders  it  impossible  for  the  brick  to 
confine  it. 

Of  the  three  states  of  matter,  solid,  liquid,  and  gas- 
eous, only  the  first  is  rigid,  and  the  last  two  fluid.   The  dis- 


HARDNESS   OF    BRICK  AND   THEIR  RESISTANCE  TO    FROST.  17 

I'uptiug-  substance  must,  therefore,  enter  as  a  liquid  or  a 
gas,  and  then  throusjli  ordinary  change  in  conditions,  be- 
come solid  within  the  bi'ick.  As  at  ordinary  temperatures, 
common  g^ases  do  not  reach  the  solid  state,  they  need  not 
be  considered. 

A  liquid  may  be  solidified  by  lowering  its  temperature, 
by  changing  the  pressure  upon  it,  or  by  evaporation  of  one 
or  more  of  its  constituents.  When  a  solid  is  dissolved,  it 
becomes  to  all  intents  and  purposes  a  liquid.  Conversely, 
when  it  is  crystallized  from  solution  it  becomes  solid  again 
and,  if  absorbed  when  in  solution,  may,  upon  the  evapora- 
tion of  the  solvent,  be  confined  within  the  brick.  Seger''^ 
states  that  the  concentration  of  the  salts  in  the  surface 
layer  of  brick  by  the  evaporation  of  water  often  causes 
the  destruction  of  the  surface.  Other  observers  have  made 
the  same  statement.  Tt  would  seem  at  first  sight  that  it 
would  be  impossible  for  a  crystallizing  salt  to  exert  any 
pressure  or  cause  any  strain,  for  as  the  crystal  grows  it 
shuts  off  automatically  the  supply  of  solution.  It  would 
thus  completely  close  the  pores,  preventing  the  further 
growth  necessary  to  cause  strain.  Recent  experiment^  has 
shown,  however,  that  growing  crystals  can  exert,  consider- 
able pressure  and  Avill  continue  to  grow  even  under  con- 
siderable resistance.  It  is  possible,  therefore,  that  brick 
may  be  injured  by  the  crystallization  of  salts  in  the  surface 
layers.  It  is  believed,  however,  that  this  is  a  minor  factor 
in  the  weathering  of  brick,  and  that  the  greater  destruction 
results  from  another  source. 

Some  substances,  such  as  water,  expand  as  tliey  pass 
from  the  liquid  to  the  solid  state.  Increase  in  pressure 
lowers  their  freezing  point.  Consequently,  Avhen  such  a 
liquid  is  confined  while  freezing,  the  increase  in  volume  will 
cause  a  pressure  upon  the  walls  of  the  confining  vessel.  In 
order  that  this  may  be  effective  in  the  brick,  it  is  necessary 


Coll.  Writings,  p.  372. 

G.   F.   Becker  and   A.   L.   Day,   Trans.  Washington  Acad,   of  Sci. 
Vol.  7. 


18  HARDNESS   OF   BRIOK   AND   THEIR   RESISTANCE  TO   FROST. 

that  enough  of  the  liquid  become  solid  to  seal  the  surface 
pores,  and  thus  make  it  possible  for  the  liquid  to  be  con- 
fined while  freezing.  In  so  doing,  a  strain  is  set  up  within 
the  brick,  which  if  great  enough,  may  burst  its  bonds  and 
cause  damage. 

It  is,  then,  to  liquids  that  expand  upon  solidification 
that  we  may  look  for  the  principal  cause  of  the  observed 
weakening  of  brick  by  changes  of  temperature.  Of  this 
class  of  liquids,  there  is  only  one  that  is  universally  abund- 
ant and  solidifies  at  ordinary  temperatures.    This  is  water. 

PHYSICAL  PROPERTIES  OF  WATER. 

Change  of  volume  with  change  of  temperature. 

The  great  majority  of  substances  contract  as  their 
temperature  is  lowered.  Water  confonm?  to  this  rule  until 
the  temperature  of  about  39  degrees  F  is  reached.  At  this 
point  water  ceases  to  contract  and  as  the  temperature  is 
lowered  further,  expands  until  it  solidifies.  Generally 
solidification  takes  place  at  32  degrees  F  but  may  be  de- 
layed— as  will  be  explained  later — until  a  lower  tempera- 
ture is  reached.  This  expansion  has  been  measured  down 
to  18  degrees  F,  and  is  at  this  temperature  .00186  units.^ 
That  is  to  say,  one  cubic  inch  of  water  measured  at  39  de- 
grees F  becomes  1.00186  cubic  inches  when  cooled  to  18 
degrees  F  without  freezing.  Since  water  is  nearly  incom- 
pressible, this  small  expansion  of  the  water,  if  it  were 
rigidly  confined,  would  cause  a  pressure  of  over  500  pounds 
to  the  square  inch. 

Change  in  volume  upon  freezing. 

When  water  changes  to  its  solid  form,  ice,  its  volume 
increases  approximately  one-tenth.  That  is,  ten  cubic 
inches  of  water  at  32  degrees  F  will  become  eleven  cubic 
inches  when  frozen.  This  increase  in  volume,  whenever 
the  freezing  water  is  confined,  may  give  rise  to  a  pressure 
upon  the  walls  of  the  containing  vessel  that  may  be  great 
eiiouah  to  burst  it. 


Chwolson,  Lehrbiick  der  Physik,  vol.  2,  p.  134. 


, HARDNESS  OF   BRICK   AND  THKIK  RESISTANCE   TO   FROST.  19 

Near  the  close  of  the  eighteenth  ceutury,  Major  Wil- 
liams, while  stationed  at  Quebec,  filled  two  13-in(h  bomb 
shells  with  water  and  closed  the  fuse  holes  b}^  driving  in  as 
tightly  as  possible  iron  plugs  weighing  three  pounds  each. 
The  shells  were  then  exposed  to  the  cold  of  the  winter  night 
about  twenty  degrees  below  zero  F.  The  next  morning 
one  of  the  shells  was  found  to  have  burst  and  a  thin  fringe 
of  ice  projected  through  and  beyond  the  crack.  The  plug 
of  the  other  shells  was  found  at  a  distance  of  415  feet  and 
a  column  of  ice  eight  inches  long  protruded  from  the  fuse 
hole.^*^.  Evidently  a  powerful  pressure  had  resulted  from 
lowering  of  the  temperature  of  the  confined  water. 

Assuming  that  all  of  the  water  froze,  and  the  shell  re- 
mained intact,  which  is  possible  if  the  shell  was  only  partly 
filled,  leaving  enough  s])ace  for  the  ice  to  form,  both  shell 
and  ice  would  contract  as  they  cooled.  Since  the  coeffi- 
cients of  expansion  of  ice  and  cast  iron  are  practically  the 
same,  whatever  pressure  may  have  been  witliiu  the  shell 
could  not  change  materially.  Consequently,  if  the  shell 
did  not  give  way  at  the  moment  the  last  of  the  water  froze, 
further  cooling  could  not  cause  its  bursting. 

If  the  water  began  to  freeze  and  the  pressure  resulting 
from  the  increase  in  volume  of  the  forming  ice  became 
great  enough  to  lower  the  freezing  point  of  the  remaining 
water  progressively  witli  its  falling  temperature,  an  in- 
creasing i)ressure  would  accumulate  within  the  shell  as  the 
water  cooled.  An  inciease  in  pressure  of  one  atmosphere 
— 15  pounds  to  the  square  inch — upon  water  will  lower  the 
freezing  point  .01388  of  a  degree  F.  The  pressure  neces- 
sary to  prevent  freezing  at  31  degrees  F  is  1080  ])ounds,  or 
half  a  ton,  to  the  square  inch;  at  22  degrees,  10800  pounds; 
at  zero,  34500  ])()un(ls;  and  at  minus  20  degrees — the  tem- 
perature of  the  air  in  Major  AYilliams'  ex])erini<'nt — 00480 
pounds,  or  over  thirty  tons,  to  the  square  inch.  This  cer- 
tainly would  be  pressure  great  enough  to  account  for  the 
bursting  of  the  shells.     It  s(^ems  probable,  therefore,  thai 


Carnot's  Physics,  13th  Ed.  Trans.,  p.  320. 


20  HARDNESS  OK    BRICK   AND   THEIR    RESISTANCE  TO   KROSfl'. 

part  of  the  water  was  still  liquid  at  the  time  the  shells 
burst,  aud  that  they  were  ruptured  bv  the  cumulative  pres- 
sure that  prevented  this  water  from  freezing. 

Moussan"  performed  an  experiment  that  throws  some 
light  upon  this  question.  He  had  a  strong  cylinder  made 
that  was  closed  at  the  lower  end  by  a  small  cone  held  in  by 
a  screw-nut,  and  at  the  upper  end  by  a  piston  moved  by  a 
screw-nut.  Removing  the  bottom  nut  and  cone  he  filled 
the  cylinder  with  water,  placed  a  bit  of  copper  rod  in  it  as 
an  index,  and  allowed  the  water  to  freeze  by  exposing  the 
apparatus  to  the  winter  air.  He  then  carefully  cleaned 
away  enough  of  the  ice  to  allow  him  to  put  the  bottom  cone 
and  nut  in  place,  screwing  them  down  as  tightly  as  pos- 
sible. Then  he  inverted  the  cylinder  and  placed  it  in  a 
salt  and  snow  mixture  at  a  temperature  of  about  zero  F. 
By  slowly  turning  the  top  screw  he  compressed  the  ice  to 
about  0.87  of  its  original  volume.  This  required  about  four 
hours.  Then  keeping  the  cylinder  in  the  cold  he  opened  its 
bottom. 

The  index  at  the  beginning  of  the  experiment  was  in 
the  upper  part  of  the  ice.  If  the  ice  remained  solid  during 
the  compression,  the  index  should  remain  in  this  position 
and  when  the  cylinder  was  opened  appear  last.  If  the  ice 
was  melted  by  the  pressure,  the  index  would  sink  through 
the  water  formed  and  should  be  at  the  bottom  of  the  cylin- 
der, appearing  first  when  it  was  opened.  When  ^[oussan 
opened  the  lower  screw,  and  loosened  the  cone,  it  came  out 
rather  .suddenly  and  ice  formed  instantly  upon  its  sides. 
Immediately  behind  it  followed  the  index  and  then,  for  the 
first  time,  came  a  thick  cylinder  of  ice  which  must  have 
formed  at  the  instant  of  opening. ^^ 


'iPogg.  Annalen,  vol.  105,  1858,  p.  170. 

'-"  ALs  man  nocli  dieseni  Verfahneu  die  iiutere  Sclduss-soliraube 
immer  in  voller  Kalte  ofifuete.  iind  den  klienen  Konns  losfe,  trat  der 
selbe  sofort  etwas  heraus  und  an  seiner  seite  bildete  sich  augenblick- 
lich  Eis.  Gleich  hinter  den  Koniis  folgte  der  Index  und  erst  nach  diesem 
ein  dichter  Eiscylinder,  der  sich  im  augenblick  des  Oeffnens  gebildet 
haben  musste." 


HARDNESS  OF    BRICK   AND  THKIK   RESISTAXCE  TO    FROST.  21 

Cousequently  he  had  proved  that  it  is  passible  to  melt 
ice  bA'  pressure  aloiie.  It  seems  probable  iu  the  light  of  his 
experiment  that  when  the  enclosing  vessel  is  strong  enough 
to  resist  the  pressure  resulting  when  ice  first  begins  to 
form,  that  the  pressure  lowers  the  freezing  point  of  the 
remaining  water  pi'ogressively  with  its  decreasing  temper- 
ature, and  therefoi'e  the  pressure  increases  as  the  tempera- 
ture is  lowered.  It  lias  been  proven  by  Tammann  and 
others  that  if  the  pressure  be  great  enough  and  tempei'ature 
low  enough,  the  ice  will  change  its  form,  but  these  condi- 
tions are  beyond  the  tenii)eratures  and  pressures  ordinarily 
prevalent.  Recognizing,  therefore,  that  there  is  a  limit, 
the  statement  nevertheless  holds  good  that  under  ordinary 
circumstances,  the  pressure  resulting  from  freezing-  water, 
when  it  is  confined,  increases  as  the  temperature  is  lowered. 

.    i 
DISINTEGRATING  EFFECTS  OF  FREEZING  WATER. 

W'licn  water  is  confined,  therefore,  and  cooh'd  below  its 
freezing  point,  it  nun-  cause  damage  either  by  its  sudden 
expansion  when  freezing  or  from  the  pressure  resulting 
from  its  attempt  to  freeze.  The  pressure  is  the  same  in 
either  case,  and  since  it  depends  directly  upon  the  temi)ei-- 
ature  at  which  freezing  takes  place,  may  be  calculated  from 
the  known  relations  of  freezing  point  and  pressure. 

Cojiditions  prcvcuiiufj  (J<iiii<n/<-.  It  is  cviilcnt  tliat 
if  the  pores  of  a  brick  were  tilled  witli  freezing  water 
rifiUU}!  v(nifincd,  the  lowering  of  lis  leiiiperal  iii-e  a  few 
degrees  below  the  freezing  point  would  utterly  ruin  I  he 
brick.  Yet  brick  are  not  ruined  in  ])ra(-ti(-e,  and  the 
largest  percentage  of  loss^  in  crushing  strength  of  a  well 
burned  brick  that  had  been  subjected  to  a  freezing  test 
was  only  a  trifle  over  foity  percent.  I]\i(lently  there 
are  mitigating  factors  effective  in  the  freezing  of  saturated 
bricks  that  have  not  been  considered.  These  are  in  part: 
the  pores  forming  tubes  of  capillary  size  permitting  the 
possibility  of  water  not  solidifying;  the  imperfect  sealing 
of  the  pores  and  consequent  partial  relief  of  the  pressure 


22  HAKDMWS  (JF   BKICK    AND   THKIR    KKSISTANCE   TO    FKOoT. 

through  outward  flow,  and  the  possible  draininge  of  part 
of  the  water  before  freezing,  leaving  the  pores  only  partly 
fllled. 
Overcooled  water. 

As  has  already  been  stated,  it  is  possible  to  cool  water 
below  the  freezing  point  without  the  formation  of  ice.  The 
conditions  that  favor  this  t)vercooling  are  freedom  from 
dust  and  other  suspended  matter,  freedom  from  dissolved 
air,  and  freedom  from  contact  with  ice,  and  confinement  in 
minute  quantities,  as  in  capillary  tubes. 

When  water  is  confined  in  capillary  tubes  it  is  possible 
for  it  to  overcool  further  than  it  would  otherwise.  By 
using  boiled  and  filtered  water,  Despretz  was  able  to  over- 
cool  it  several  degrees  below  the  limit  given  b}^  Chwolson^"', 
— 18° F — and  in  the  finest  tube  reached  a  temperature  of 
four  degrees  below  zero  F,  before  ice  formed.  The  tem- 
peratures reached  were  influenced  l)y  the  size  of  the  tubes, 
the  larger  ones  freezing  sooner. 

The  influence  of  ice  on  the  amount  of  overcooling  in 
capillary  tubes  is  well   illustrated  by  an  experiment  of 
Moussan's.      He  placed  two  series  of  capillary  tubes  con- 
taining boiled  water,  in  a  box,  and  exposed  them  to  winter 
cold  which  reached  a  minimum  of  about  22  degrees  F   One 
series  was  placed  in  an  inclined  position,  with  one  end  )pen 
in  a  vessel  of  water.    The  other  series  was  placed  in  a  hori- 
zontal position  and  the  ends  sealed  with  shellac  to  prevent 
evaporation.    All  of  the  latter  series  above  1-27  of  an  inch 
in  diameter  froze.     In  the  series  placed  in  the  water  and 
therefore  in  contact  with  ice  as  it  formed  in  the  vessel,  onlyj 
those  smaller  than  1-75  of  an  inch  in  diameter  escapee 
freezing.    Considering  the  relatively  small  amount  of  over-j 
cooling  in  this  case,  it  is  evident  that  only  the  Avater  in! 
very  small  tubes  is  capable  of  being  overcooled  in  contactj 
with  ice. 

The  water  in  the  pores  of  brick  is  never  free  from  dust 
and  dissolved  air,  and  the  brick  are  continually  subjectec 


i^Chwolson.  Lehrbuck  der  Phj'sik,  vol.  3,  p.  592. 


HAIMi.NKSS   OK    IJHll'K    A  N  I  >   T 11  iO  1  K  HKSISTA  NCE  TO  KKOS'l'.  23 

shock  and  vibration  from  the  traffic  in  the  streets  and 
buildinjj;.  The  water  on  the  outer  face  certainly  freezes 
and  the  water  in  the  pores  is  in  contact  with  ice  as  a  con- 
sequence. On  the  other  hand,  most  of  the  pores  are  very 
small  or  at  least  the  numerous  constrictions  in  them  pro- 
duce the  same  effect. 

As  there  is  no  method  known  at  present  by  which  tlie 
actual  freezing  of  water  in  the  pores  can  be  proven  beyond 
question,  we  are  compelled  to  depend  upon  indirect  reason- 
ing. It  is  known  that  brick  suffers  a  loss  in  strength  by 
having  been  subjected  to  freezing.  The  amount  of  this 
loss  increases  with  the  fineness  of  the  pores — as  shown  by 
the  results  of  the  present  freezing  tests — and  not  with  their 
coareness,  as  it  should  if  overcooling  was  the  dominant  fac- 
tor. It  has  been  shown  that  there  is  nothing  inherent  in 
brick  that  will  cause  this  loss,  and  that  the  only  important 
cause  is  the  pressure  resulting  from  freezing  water.  Loss 
of  strength  in  the  brick  has  been  reported^in  all  properly 
conducted  freezing  tests,  although  in  these  a  wide  range  in 
the  temperatures  has  been  used.  It  seems  extremely  prob 
able,  therefore,  that  at  least  some  of  the  water  freezes  and 
causes  danmge.  The  amount  of  damage  done,  {\ssuming 
the  pores  to  be  full  and  unable  to  drain,  undoubtedly  de- 
pends on  the  temperature  and  the  relative  size  of  the  pores, 
since  the  finest  pores  freeze  last  and  at  the  lowest  temper- 
atures. It  is  possible  that  a  portion  of  this  loss  of  strength 
may  be  due  to  incipient  fractures  caused  by  the  rapid  and 
repeated  heating  and  cooling  to  which  the  brick  were  sub- 
jected. 
fiiiprrfed  scaJinti  of  tlje  Hurfufc  pores. 

Obviously  the  power  of  resistance  of  the  walls  of  the 
containing  vessel  is  no  greater  than  that  of  its  weakest 
point.  AVhen,  as  in  the  case  of  the  bombshell  exposed  in 
Canada,  the  plug  failed  before  the  walls  of  the  shell,  the 
freezing  water,  instead  of  bursting  the  shell  found  relief 
by  extruding  a  column  of  ice  through  the  fuse  hole.  If  a 
bottle  is  filled  and  not  too  tightly  corked,  it  will  present  the 
same  phenomenon  when  the  water  is  frozen.    Evidently,  if 


\.^ 


24  HARDNESS  OF   BRICK    AND   THEIR   RESISTANCE  TO   FROST. 

the  pores  at  the  surface  of  the  brick  are  completely  sealed 
by  the  first  formed  ice,  the  ajnouiit  of  damage  done  depends 
plugs  or  spicules  beyond  the  immediate  surface  of  the 
brick. 

Mosely^^  determined  the  tenacity  of  ice  as  about  100 
pounds  to  the  square  inch.  This  was  measured  as  the  ice 
was  melting.  Andrews^^'  measured  the  resistance  offered 
by  a  block  of  ice  to  penetration  by  a  heavily  loaded  iron 
rod  at  different  temperatures.  He  found  that  the  ice  was 
very  hard  and  resistant,  allowing  scarcely  any  penetration, 
at  the  temperatures  from  minus  thirty  to  ten  degrees  F. 
At  ten  degrees  it  became  slightly  softer,  gradually  soften- 
ing until  about  twenty  degrees  was  reached.  The  softening 
now  became  more  rapid  until  near  the  melting  point,  when 
it  bcame  vei\y  rapid.  Tammann^'^  found  that  the  plastic- 
ity of  ice  is  relatively  small  but  increases  near  the  melting 
point. 

It  is  evident  that  the  resistance  offered  by  the  ice 
plugs  when  they  are  first  formed  is  quite  small.  As  the 
temperature  falls,  however,  their  rigidity  increases  rapidly 
and  when  the  temperature  is  lowered  sufficiently,  may  be- 
come rigid  enough  to  withstand  the  pressure  of  the  freezing 
water  in  the  interior  of  the  brick.  The  irregular  shape  of 
the  pores  is  an  important  aid  to  the  plugs  in  maintaining 
their  position  at  the  outlets  of  the  pores.  As  the  cooling 
of  the  brick  progresses  slowly  into  the  interior,  the  tem- 
perature of  the  ice  plugs  has  probably  fallen  several  de- 
grees by  the  time  the  interior  water  begins  to  freeze.  Tak- 
ing into  consideration,  therefore,  the  increased  strength  of 
the  plug  due  to  this  decrease  in  temperature,  and  the  ex- 
treme irregularity  of  shape  of  the  pores,  it  is  believed  that 
there  is  but  little  relief  of  pressure  due  to  exuding  of  the 
pugs  or  spicules  beyond  the  immediate  surface  of  the  brick. 


J^Phil.  Mag.,  p.  39,  1870. 

'"Quoted  by  Barnes,  op.  cit. 

i6Ann.  der  Physik,  vol.  7,  1902,  p.  208. 


HAKDNKSS   OF   BKICK    AM>   THKIK    KKSISTANCK   TO    KKOST.  25 

Partiul  druhiufjc. 

It  is  evident  that  if  a  pore  were  ouly  niiie-tentlis  full, 
expansion  of  the  forming  ice  could  take  place  without  in- 
jury to  the  pore.  Xo  pressure  can  arise  within  the  pore 
until  it  is  more  than  nine-tenths  tilled,  for  this  leaves  suffi- 
cient space  for  expansion  of  the  ice  or  water.  If,  after 
pores  and  cavities  are  filled,  it  is  possible  for  one-tenth  of 
the  water  to  drain  before  it  freezes,  they  will  be  removed 
from  danger  of  rupture  and  no  damage  can  result.  The  two 
factors  that  govern  the  amount  of  water  in  the  pores  and 
cavities  when  the  plane  of  frost  reaches  them  are :  1st,  the 
completeness  with  which  the  pores  are  sealed,  and  2nd  the 
rate  of  flow  of  the  water  through  the  pore  system. 

It  goes  without  saying  that  if  brick  are  not  completely 
sealed  on  all  sides,  the  pressure  within  maj'^  be  relieved  by 
the  flow  of  the  water  from  the  open  sides.  In  freezing  tests, 
as  usually  conducted,  the  brick  are  exposed  to  cold  on  all 
sides  alike.  As  they  lose  their  heat,  they  cool  simultan- 
eously on  all  surfaces,  thereby  freezing  and  sealing  the 
pores  on  all  sides  at  the  same  time,  and  completel.y  enclos- 
ing the  remaining  water  within  the  brick. 

In  the  case  of  brick  laid  in  the  wall,  this  is  not  true. 
The  outside  face  becomes  chilled  long  before  the  others,  and 
while  the  pores  on  the  surface  are  sealed,  the  others  are  left 
open,  offering  a  passage  for  the  water  as  pressure  in- 
creases. Consequently  the  freezing  test  puts  the  brick  un- 
der conditions  to  which  those  in  the  wall  are  never  sub- 
jected. 

A  brick  saturated  with  water  and  placed  in  a  position 
where  it  is  possible  for  it  to  drain,  but  where  evaporation 
is  prevented,  will  lose  but  a  very  small  amount  of  water.  A 
series  of  the  brick  tested  were  placed,  after  saturation,  in 
such  a  position,  and  at  the  end  of  forty-eight-  hours  had 
lost  but  one  or  two  grams  of  water.  Consequently,  when 
the  brick  are  frozen  in  the  freezing  can,  they  do  not  drain. 
But  as  it  is  impossible  to  completely  saturate  brick  by 
soaking,  certain  parts  are  free  from  water.  When  ice  be- 
gins to  form  and  the  ice  plugs  have  become  strong  enough 
to  resist  the  growing  pressure  of  the  freezing  water,  relief 


26 


HA.KDNESS  OF  BKICK  AND   THEIK    KESISTANCK   TO    FROST. 


is  had  by  the  flow  of  part  of  the  water  into  the  vacant 
spaces.  The  relative  amount  of  damage  done  in  the  brick 
depends  upon  the  ease  and  rapidity  with  which  this  is  ac- 
complished. As  the  resistance  to  flow  increases  rapidly 
with  the  decrease  in  the  effective  diameter  of  the  pores,  the 
finer  pored  brick  should  suffer  the  greater  loss  in  freezing. 

Flow  throuijli  capillary  tubes.  The  pores  of  the  brick 
are  not  of  course  perfect  capillary  tubes,  but  it  has  been 
shown  that  they  obey  the  same  laws.  The  truths,  therefore, 
will  be  at  least  approximated  by  considering  them  as  such. 

The  volume  of  flow  of  a  liquid  through  a  capillary  tube 


in  a  unit  of  time  is  expressed  by  the  formula 


in  which 


r  is  the  radius  of  the  tube,  p  is  the  pressure,  or  unbalanced 
force,  at  the  end  of  the  tube,  u  is  the  viscosity,  or  resistance 
to  flow  of  the  liquid  used,  and  I  is  the  length  of  the  tube. 
Expressed  in  words,  the  formula  means  that  the  amount  of 
flow  in,  say  a  second,  increases  sixteen  times  when  the 
radius  of  the  tube  is  doubled,  is  doubled  when  the  pressure 
is  doubled,  is  halved  when  the  viscosity  of  the  liquid  is 
doubled,  and  is  halved  when  the  length  of  the  tube  is 
doubled. 

The  velocity  of  flow  may  be  determined  by  dividing 
the  total  flow  by  the  area  of  the  cross  section  of  the  tube. 

Velocity  or  V=:  ^> — j-  h-  tt  r  - 


This  means  that  if  the  pressure,  viscosity  of  the  water, 
and  the  length  of  the  pores  were  equal,  a  pore  twice  the 
size  of  another  would  transmit  water  four  times  as  fast. 
Therefore  the  coarser  pores  of  a  brick  would  offer  the  least 
resistance  to  the  flow  of  water  through  them. 

Effect  of  laminations  upon  the  durahility  of  hrick. 
The  laminations  are  irregularly  scattered  through  the 
brick,  and  as  a  result,  the  water  is  not  uniformly  distri- 
buted but  the  greater  portion  of  it  is  concentrated  in  these 
cavities.  The  volume  of  water  in  the  laminations  is  enor- 
mously greater  than  that  in  the  pores.    Consequently  the 


HARDNESS  OF   BRICK   AND   THEIR   RESISTANCE  TO    KKOST.  2( 

amount  of  expansion  due  to  freezing  is  not  only  greater, 
but  it  is  concentrated  at  one  point.  Further,  the  lamina- 
tions extend  over  a  relatively  large  area  and  so  weaken  the 
brick  that  much  more.  On  account  of  the  greater  amount 
of  expansion  and  the  smaller  resistance  offered  by  the  brick 
at  these  points,  the  greater  amount  of  damage  is  done  by 
water  in  the  laminations. 

The  laminations  are  connected  with  each  other  and  the 
surface  of  the  brick  only  through  the  pores.  The  rapidity 
with  which  they  are  filled  and  drained,  is  governed  by  the 
size  of  the  pores  and  that  alone.  As  with  the  pores,  the 
amount  of  damage  that  is  done  depends  upon  the  complete- 
ness with  which  the  laminations  are  filled.  Therefore,  it 
follows  that  the  durability  of  brick  depends,  not  upon  the 
number  or  size  of  the  laminations,  but  upon  the  effective 
diameter  of  the  connecting  pores.  As  these  form  the  greater 
part  of  the  total  pore-space,  it  is  now  clear  why  the  dura- 
bility of  brick  does  not  run  parallel  to  the  total  pore-space. 

As  the  hardness  of  brick  increases,  the  effective  diame- 
ter of  the  pores  decreases,  and  tenacity  and  brittleness  in- 
creases. The  effect  of  decrease  in  the  effective  diameter  of 
the  pores  is  to  increase  the  resistance  offered  to  the  flow  of 
water  through  the  pores,  the  increase  of  tenacity  gives 
greater  strength  to  resist  the  expansion  of  the  forming  ice, 
and  the  increased  brittleness  decreases  the  limit  to  which 
the  brick  may  be  strained  without  rupture.  Consequently 
the  harder  burned  brick  may  be  expected  to  suffer  the 
greater  relative  loss  in  a  freezing  test,  whenever  the  effects 
of  the  smaller  pores  and  the  greater  brittleness  overcomes 
the  increased  strength.  Even  when  this  is  the  case,  it  does 
not  necessarily  mean  that  the  harder  brick  are  the  poorer, 
for  as  a  rule  their  increased  strength  gives  a  large  factor  of 
safety,  and  even  after  they  have  lost  forty  percent  of  their 
original  strength,  they  are  often  much  stronger  than  is 
required. 

Relative  coniraction  of  hrick  and  ice.  After  ice  is 
formed,  the  further  damage  it  will  do  to  the  brick  depends 
upon  their  relative  rates  of  contraction.    The  coefficient  of 


28  HARDNESS  OF  BKICK  AND  THEIK  RESISTANCE  TO  FROST. 

expansion^'  of  clay  wares  is  .00000457  and  that  of  ice 
.0000350.  This  means  that  ice  will  contract  nearly  nine 
times  as  fast  as  brick,  and  will  shrink  away  from  the  walls 
of  the  pores  as  the  temperature  is  lowered.  Therefore  ice 
can  damcujc  brick  only  at  the  time  of  its  formation. 

CONDITIONS  GOVERNING  THE  BRICK  IN  THE  WALL. 

The  conditions  under  which  brick  are  placed  varies  in 
different  parts  of  the  wall.  In  the  foundation,  below  the 
water  line,  brick  are  subject  to  continual  immersion  in 
water,  and  under  these  circumstances  must  sooner  or  later 
become  fully  saturated.  In  this  part  of  the  wall,  there  is 
no  chance  for  any  drainage,  and  the  only  factors  that  are 
called  into  play  are:  the  total  amount  of  pore-space,  and 
the  greatest  strength.  These  bricks  are  those  that  have 
been  burned  hardest,  and  in  this  situation  are,  beyond 
doubt,  the  ones  that  should  be  used. 

Just  above  the  water  line,  capillarity  determines  the 
amount  of  water  contained.  The  height  at  which  water 
stands  in  a  capillary  tube,  depends  upon  the  diameter  of 
the  tube.  The  smaller  the  tube,  the  greater  is  the  height. 
Consequently,  in  walls  footed  in  a  constant  source  of  sup- 
ply, water  will  ascend  higher  when  built  of  finer-pored 
brick,  than  when  built  of  brick  with  larger  pores.  The 
finest-pored  brick  are  the  slowest  to  pass  on  to  the  founda- 
tion, the  water  received  from  above.  On  this  account,  also, 
finer-pored  brick  are  saturated  to  a  greater  height  above 
the  water  line  than  the  coarser-pored  bricks.  On  the  other 
as  the  conditions  are  practically  those  of  saturation,  the 
gain  in  strength  of  the  harder  burned  brick  over  the 
coarser-pored  ones,  more  than  offsets  the  advantage  of  a 
narrower  saturation  zone  afforded  by  the  latter. 

Above  the  zone  where  capillarity  is  dominant,  the 
brick  obtain  water  only  from  atmospheric  precipitation, 
and  leakage  from  pipes  and  gutters.     Here  the  conditions 


i^Castell  Evans,  Phys.  Chem.  Tables,  p.  147. 


HARDNESS  OF   BRICK  AND  THEIR   RESISTANCE   TO    FROST.  29 

are  those  of  drainage,  and  the  brick  that  can  rid  itself  of 
water  most  quickly  is  most  likely  to  endure..  The  velocity 
with  which  water  passes  through  a  brick  depends  entirely 
upon  the  size  of  the  pores.  Therefore,  in  this  situation, 
coarser-pored  brick  should  be  used,  since  they  transmit 
water  faster. 

The  three  different  situations  in  which  brick  are 
placed  in  a  wall  are :  the  saturated  zone  below  the  water 
line,  the  capillary  region  just  above,  and  the  drainage  zone 
above  these.  (See  figure  la.)  In  designing  freezing  tests, 
the  difference  in  the  situations  in  which  brick  are  to  be 
placed  should  be  taken  into  account,  and  the  tests  should 
indicate  the  brick  best  suited  to  each  of  these  positions. 
This  has  not  been  generally  recognized,  and  as  a  conse- 
(pieuce  many  brick  that  are  well  suited  for  certain  condi- 
tions are  condemned,  because  the  tests  used  are  the  same 
for  all  situations.  Thus  the  coarser-pored  brick,  which  are 
really  best  for  situations  where  drainage  is  the  dominant 
factor,  are  unjustly  condemned  on  account  of  their  high 
porosity.  The  claim  is  constantly  made  that  certain  build- 
ing materials  will  not  withstand  the  frost,  simply  because 
they  are  porous  and  absorb  water  rapidly.  It  is  evident 
that  this  material,  in  a  position  where  it  can  drain,  will  be 
freed  from  danger  of  freezing  much  more  rapidly  than  one 
that  absorbs  water  slowly,  and  therefore  drains  slowly. 

It  is  true  that  the  coarser  material  will  pass  water 
through  the  wall  to  the  interior  much  more  rapidly  and 
abundantly  than  that  which  is  finer.  If  the  amount  trans- 
mitted is  greater  than  the  air  in  the  interior  can  absorb, 
the  walls  will  be  damp.  This  is  another  problem  entirely, 
and  has  nothing  to  do  with  resistance  to  frost.  Therefore, 
in  considering  only  the  powers  of  a  building  to  withstand 
weather,  the  conclusion  is  obvious  that  in  situations  above 
the  saturated  zone,  coarser-pored  brick  are  better,  provided 
they  are  burned  sufficiently  to  remove  them  from  the  soft 
salmon  class. 


30 


HARDNESS  OF   BBICK   AND  THEIK   KKSISTANCE   TO    FKOST. 


TRANS. AM  CER  SOC  VOL.IX 


JONES,    PLATE     lA 


I 
I 


Zone  of 


-iV^terL/ne 


Ideal  Sketch  Showing  Normal  Distribution  of  Water  in  a  Brick  Wall. 


HARDNKSS   OK    HKK'K  AND  THEIK   RESISTANCE   TO    FROST.  31 

FREEZING  TeSTS. 

Recognizing-  the  different  conditions  under  which 
brick  are  placed  in  a  wall,  tests  should  be  designed  with 
these  conditions  in  view.  The  important  factors  to  be  de- 
termined in  brick  to  be  placed  in  the  zone  of  saturation,  or 
in  similar  situations,  are  total  pore-space  and  strength. 
The  factor  of  greatest  importance  in  brick  to  be  placed  in 
the  zone  of  drainage,  is  rate  of  flow  of  water  through  the 
pores.  As  long  as  the  brick  possesses  strength  enough  to 
carry  its  load  with  a  safe  margin,  further  strength  is  not 
necessary.  The  question  here  is  not  one  of  amount  of  porc- 
spacc,  but  size  of  pores.  These  should  be  sufficiently  large 
to  permit  proper  drainage,  thus  preventing  danmge  to  the 
brick  by  frost. 

Methods  of  determining  pore-space.  The  common 
method  of  determining  pore-space  is  to  place  the  brick  in 
water,  and  after  a  certain  time,  determine  the  amount  of 
water  absorbed.  This  is  considered  as  efpiivalent  to  the 
total  pore-space.  When  a  brick  absorbs  water,  it  is  neces- 
sary for  the  enclosed  air  to  flow  out  and  water  flow  in 
through  the  pores.  The  rapidity  with  which  this  takes 
place  depends  upon  the  effective  diameter  of  the  pores.  If, 
during  this  process,  any  air  remains  in  the  pores  and  cavi- 
ties, and  is  surrounded  by  the  entering  water,  its  only 
method  of  escape  is  by  diffusion  through  tlie  water.  This 
is  a  very  slow  process  as  compared  with  flow. 

It  lias  been  observed  that  a  bri(k  will  gain  in  weight 
when  left  in  water,  even  after  a  iiionth's  time.''*  Part  of 
this  gain  is  probably  due  to  bacteria,  and  other  minute  or- 
ganisms, that  colonize  and  multiply  within  the  brick. 
When  a  surface  is  exposed  to  the  air,  water  evaporates,  and 
may  deposit  salts  within  the  brick.  The  greater  part  of 
the  gain,  notwithstanding  these  other  sources,  is  due  to  the 
diffusion  of  imprisoned  air,  and  its  replacement  by  water. 

As  an  illustration  of  this  point,  two  of  the  series  of 
brick  tested  were  placed  in  water  three  inches  deep  and 


wwheeler,  Mo.  Geol.  Surv.,  Vol.  11. 


82 


HARDNESS  OK    BRICK   AND  THEIR   RESISTANCE   TO   FROST. 


allowed  to  .stand  fortjreiglit  hours.  After  weighing  and 
re-drying,  they  were  placed  in  water  onlj'  one  inch  deep,  for 
the  same  length  of  time.  Using  the  amount  of  water  ab- 
sorbed during  deep  immersion  as  one  hundred  percent,  the 
percentage  of  water  absorbed  during  shallow  immersion 
was  found  to  be  as  follows : 


Kind  ot  Brick 

Soft 

Med.  Soft 

Med.  Hard 

Hard 

Soft  mud  shale 
Wire  cut  shale 

163.2% 

95.5% 

120.6% 

98.5% 

91.5% 

43.3% 

70.9% 

46  3% 

The  coarser-pored  brick  had  absorbed  much  more  dur- 
ing shallow  immersion  than  during  deep  immersion,  while 
the  finer-pored  had  not  absorbed  so  much.  When  a  brick 
was  deeply  immersed,  water  flowed  in  from  the  sides, 
above  the  air  in  the  bottom  of  the  brick,  before  it  had  a 
chance  to  escai)e.  Replacement  of  the  entrapped  air  could 
only  be  accomplished  b}^  ditfusion.  In  shallow  immersion, 
the  air  had  a  chance  to  escape  through  the  pores  above,  and 
was  forced  out  by  the  ascending  water. 

Another  factor  in  the  experiment  is  the  relation  of 
floAv  to  pressure.    It  will  be  noticed  in  the  formula  express- 

mg  the  velocity  of  flow  in  capillary  tubes     g — .     that  the 

flow  increases  when  the  pressure  is  increased.  The  pres- 
sure of  the  water  on  the  bri(*k  was  twice  as  great  in  th(^ 
deep  immersion  as  in  the  shallow.  The  water,  therefoi-e, 
flowed  in  twice  as  fast  through  th(;  pores  during  deep  im- 
mersion. In  addition,  the  area  exposed  for  the  entrance  of 
water  was  nearly  three  times  as  great,  and  therefore  many 
more  pores  were  available  for  the  entrance  of  the  water. 
It  is  this  effect  that  masks  the  imprisonment  of  air  in  finer- 
pored  brick,  and  it  was  in  spite  of  this  that  the  more  rapid 
flow  and  trapping  of  air  took  place  in  the  coarser -pored 
brick. 

Many  investigators  have  maintained  that  complete  im- 
mersion is  the  only  natural  method  by  which  the  relative 


HARDNESS  OK    BRICK   AND  THEIR   RESISTANCE    TO   FROST.  33 

porosity  of  brick  sliould  be  tested,  since  it  is  by  soaking 
tliat  a  brick  becomes  filled,  when  it  is  in  a  wall.  It  is  true 
that  brick  in  the  zone  of  saturation,  where  they  are  contin- 
ually in  contact  with  water,  become  saturated  by  this 
method.  The  length  of  time  thej  are  in  contact  with  the 
water  is  not  taken  into  account,  however,  nor  the  fact  that 
the  air  imprisoned  at  the  first  filling  of  the  pores  slowly 
dittiises  until  only  the  amount  held -in  solution  by  the 
water  is  left.  Brick  in  this  situation  become  eventually  as 
thoroughly  saturated  as  if  all  the  air  had  been  removed 
and  replaced  by  water  in  the  first  place.  This  complete  re- 
placement of  the  air  is  not  possible  by  complete  immersion 
for  the  short  time  given  in  the  usual  absorption  test.  As 
the  only  object  in  finding  the  pore-space  is  to  determine  its 
total  amount,  in  order  to  judge  the  relative  durability  of 
brick  in  situations  of  complete  saturation,  the  value  of  this 
method  is  small  except  as  a  rough  test. 

Wlieuever  the  method  of  soaking  is  used,  the  depth  of 
immersion  should  be  adjusted  to  the  rate  of  flow  of  the 
water  througli  the  pores.  This  is  illustrated  by  the  above 
experiment  where  the  coarser  pored  brick  were  more  com- 
pletely filled  by  shallow  immersion,  while  the  finer  pored 
were  better  filled  by  deep  immersion. 

The  method  that  undoubtedly  gives  the  most  accurate 
and  concordant  results  is  that  proposed  by  Dr.  Buckley.^" 
He  placed  the  specimens  to  be  tested,  after  drying  and 
weighing,  in  an  air  tight  jar  and,  after  exhausting  the  air 
as  completely  as  possible,  allowed  l)oiling  water  to  slowly 
enter  and  cover  the  stones.  This  demands  considerable 
apparatus  and  is  not  available  for  general  use  on  this  ac- 
count. It  is  possible  to  approximate  the  truth  by  placing 
the  brick,  after  drying  and  weighing,  in  a  pan  with  a  small 
amount  of  boiling  water  and  boiling  them  six  hours,  add- 
ing more  water  from  time  to  time,  until  during  the  last 
liour  of  the  test  they  are  completely  immersed.  As  heat 
decreases  the  viscosity  of  both  air  and  water,  the  flow 


'Building  and  Ornamental  Stones  of  Wisconsin,  "Wis.  Geol.  Survey. 


34  HARDNESS   OF   BRIOK   AND   THEIR   RESISTANCE  TO    FROST. 

through  the  pores  is  accelerated,  and  the  saturation  fairly 
complete  at  the  end  of  the  time.  Care  should  be  taken  to 
use  as  pure  water  as  possible,  in  order  to  prevent  the  pre- 
cipitation of  salts  in  the  brick  through  evaporation  of 
water  from  the  exposed  surfaces.  If  this  should  take  place 
the  amount  of  pore-space  determined  would  be  more  than 
the  true  pore-space.  Rain  water  or  distilled  water  is  the 
best. 
Calculation  of  pore-space. 

Having  determined  the  total  amount  of  water  ab- 
sorbed, it  is  possible  to  calculate  the  pore-space.  .  In  doing 
this,  care  must  be  taken  to  use  the  same  kind  of  units 
throughout.  For  instance,  the  common  method  is  to  divide 
the  weight  of  water  absorbed  by  the  dry  weight  of  the 
brick.  This  cannot  give  the  true  pore-space,  since  it  uses 
the  mass  of  the  brick  to  divide  the  mass  of  the  water,  a  sub- 
stance two  and  a  half  times  as  light,  volume  for  volume. 
The  result  thus  obtained  is  too  small.  To  obtain  the  cor- 
rect pore-space,  the  two  masses  must  be  reduced  to  equiva- 
lent substances,  or  volumes,  and  must  be  expressed  in 
terms  of  one  or  the  other. 

The  simplest  reliable  method  with  which  the  writer  is 
acquainted  is  one  devised  by  Mr.  Purdy.^^  This  is,  divide 
the  water  absorbed  by  the  difference  between  the  wet 
weight  of  the  l)rick  and  its  weiglit  when  suspended  in 
water.  This  gives  the  volume  of  water  absorbed  divided  l>y 
tlie  volume  of  the  brick,  or  true  pore-space.  In  determin- 
ing the  pore-space  of  the  brick  tested,  a  slightly  modified 
form  of  this  method  'was  used  which  gave,  when  carefully' 
executed,  nearly  as  accurate  results.  The  volume  was  de- 
termined by  measurement  of  the  three  dimensions,  and  this 
was  used  as  the  divisor  of  the  water  absorbed. 
Measuremeut  of  the  rate  of  floio  through  pores. 

As  has  been  stated,  the  velocity  of  flow  through  capil- 

lary  tubes  is  expressed  by  the  formula     ^     ,     in  which  r  is 


20Page  211  of  this  volume. 


HARDNESS   OF   BRICK  AND   THEIR  RESISTANCE  TO   FROST.  36 

the  radius  of  the  tube,  P  is  the  difference  iu  pressure  at  the 
ends  of  the  tube,  u  is  the  viscosity  of  the  fluid  used,  and  I  is 
the  length  of  the  tube.  When  a  brick  is  placed  in  water, 
the  force  that  causes  the  water  to  enter  and  pass  into  the 
brick,  is  the  adhesion  or  attraction  of  the  water  for  the 
walls  of  the  pores.  The  height  that  the  water  will  reach, 
depends  upon  the  mutual  attraction  of  the  molecules  at  the 
suitface  of  the  water,  or  surface  tension.  The  force  that 
causes  the  water  to  flow  is  expressed  by  the  formula 
2TrrT  cos  a,  in  which  r  is  the  radius  of  the  tube,  T  is  the 
surface  tension,  and  a  is  the  angle  of  contact  between  the 
water  and  the  walls  of  the  pore.  The  opposing  downward 
force,  due  to  the  weight  of  water  raised  in  the  pore,  is 
expressed  by  the  formula  irrVipg  in  which  h  is  the  height  to 
which  the  water  has  risen  at  any  particular  instant,  p  is 
the  density  of  the  water,  and  f/  is  the  force  of  gravity.  The 
unbalanced  force  that  causes  movement  is  equal  to  their 
difference. 

Unbalanced  force=P^=2irT  cos  a — -n-r^pg. 

Since,  in  the  equation,  all  of  the  factors  may  be  con- 
sidered as  constants  in  the  case  of  the  brick  and  water,  ex- 
cepting r  and  h,  and  designating  these  constants  as  K  and 
k  respectively,  the  equation  may  be  written 

P=Kr  —  h-V,. 

Substituting  this  value  of  P  in  the  velocity  equation, 
we  have 

Velocity=V==      gu^ 

Since  8u  is  a  constant  in  this  particular  case,  and  I 
equals  h  we  can  write  the  equation 

K.h      "^  K.\h 


F=  "•  „  ';•  "  =  ^  (-^  —kr' 


This  means  that  the  velocity  of  the  water  entering  the 
pores  of  the  brick  through  capillary  action  varies  approxi- 
mately as  the  cubes  of  the  radii  of  the  pores,  and  inversely 


36 


HARDNESS  OF   BRICK  AND   THEIR   RESISTANCE   TO   FROST. 


as  the  lieiglit  to  which  it  ascends.  Consequently  a  coarse- 
pored  brick  will  fill  much  more  rapidly  than  a  fine-pored 
one. 

As  a  test  of  this  theory,  the  three  series  of  brick  used 
in  the  freezing  tests  were  placed  in  water,  and  the  rate  at 
which  they  filled  determined  by  weighing  at  intervals  of 
Vi)  %?  I5  6,  24,  and  48  hours.  The  first  set,  the  soft  mud 
made  from  surface  clay,  were  placed  in  water  three  in^fhes 
deep.  While  some  differentiation  was  shown,  it  was 
thought  best  to  set  the  others  in  water  only  one  inch  deep, 
and  allow  capillarity  to  have  full  play.  As  was  expected, 
the  differentiation  was  more  marked.  The  results  are 
as  follows: 


Kind  of 

Grade  of 
Hardness 

Pore 

Space 

G 

ain 

Total 

BriCK 

abs'b'd. 

15  miu. 

369.0 

30min 

1  hr. 

6hrs. 

24hrs. 

10.5 

48hrs 

4.6 

Soft  mud 

Soft 

33.0% 

45.3 

5.1 

8.7 

442.0 

Surface 

Med.  s't 

26.9% 

320  9 

2.2 

2.1 

7.1 

7.6 

3  6 

343  6 

Clav 

' '   hard 

21.2% 

ii37.9 

8.1 

1.6 

7.7 

4.6 

3.2 

258  9 

Hard 

Soft 

10.3% 

26.9 

4.4 
52.7 

8.9 

37.4 

33  2 
12.5 

17 
4  2 

106  6 

Soft 

26. 2  f. 

235.1 

94.2 

50.4 

4.53  1 

Mud 

Med.  s't 

17.8 

166.8 

44.2 

68.0 

23.7 

5.0 

10 

310.1 

Shale 

"   liard 

11.6 

17.5 

9.1 

8.1 

68.2 

26.4 

1.0 

180.4 

Hard 

5.8 

4  5 

1.0 
40.4 

1.0 
64.1 

6.7 

19  2 
16  6 

16  8 
9.1 

48  4 

Wire 

Soft 

27.6% 

160.5 

111  3 

402  0 

Cut 

Med.  s't. 

17.1 

78.8 

19.4 

25.7 

89.7 

13  7 

8  4 

233.3 

Shale 

"   hard 

2.1 

3.8 

0.4 

0.9 

2.2 

2  3 

1.6 

11.1 

Hard 

0.9 

2.2 

0,3 

0.4 

0.5 

0.5 

0.7 

5.6 

Using  the  total  amount  of  water  absorbed  b}'  each 
grade  as  one  hundred,  the  percentage  absorbed  during  each 
interval  was  found  to  be  as  follows: 


HARDNESS   OF   BRICK  AND  THKIR  RESISTANCE   TO    FROST. 


37 


Gain 

Kind  of 

Grades   of 
Hardness 

Brick 

13  min. 

30  min. 

Ihr. 

6hrs. 

24  hrs. 

48  hrs 

Soft 

Soft 

83.0% 

10.3% 

1.2% 

2.0 

2.4% 

11% 

Mud 

Med.  soft 

93.4 

0.7 

0  6 

2.0 

2.2 

1.1 

Surface 

Med.  hard 

92.1 

1.2 

0.7 

3.0 

1.8 

1.2 

Clay 

Hard 

25.1 
51  9 

4.0 
11.9 

3.4 

35  0 

31.1 

1.4 

Soft 

Soft 

21.0 

11.3 

2.9 

10 

Mud 

Med.  soft 

54.2 

14.3 

21.9 

7.7 

16 

0.8 

Shale 

Med.  hard 

13.4 

7.0 

6.2 

52  3 

20.3 

0  8 

Hard 

Soft 

9.6 

2.1 

2.1 

13.8 

39.7 

3  27 

Wire 

40.0 

10.5 

15.6 

27.5 

4.1 

2.3 

Cut 

Med.  soft 

33.9 

8.5 

11  3 

38.8 

6.0 

15 

Shale 

Med.  hard 

34.5 

3.5 

8.0 

19  3 

20.5 

14  2 

Hard 

47.3 

6.4 

9.6 

10.3 

10.3 

IH.l 

Average 

Soft 

58.3 

11.0 

12.6 

13.6 

3.1 

1.5 

of 

Med.  soft 

60.5 

7.8 

11  2 

16.2 

3.3 

10 

Grades 

Med.  hard 

46.7 

3.9 

4.9 

24.9 

14.2 

5.4 

Hard 

27.3 

4.2 

5.0 

19.7 

27:0 

16  7 

Plotting  the  average  percentages  absorbed  by  the  sim- 
ilar grades  of  the  series  shows  graphically  the  relative 
rates-  with  which  the  water  was  absorbed  by  the  different 
grades  of  brick.     (See  figure  No.  2.) 

It  is  fair  to  assume  that  all  of  the  brick  in  a  series 
had  approximately  the  same  number  of  pores  before  they 
were  burned.  As  the  burn  progressed,  the  effective  size 
of  the  pores  decreased  as  is  indicated  by  the  diminishing 
pore  space.  Therefore,  the  difference  in  the  rates  of  absorp- 
tion is  a  function  of  the  size  of  the  pores  rather  than  the 
number.  The  curves  of  the  soft  and  medium  burned  brick 
show  but  little  difference.  As  has  been  stated,  the  effective 
diameter  of  the  pores  increases  during  the  period  of  dehy- 
dration and  oxidation.  As  these  brick  had  been  burned 
only  to  about  the  close  of  this  period,  their  pores  should  be 
about  the  same  size,  as  is  indicated  in  the  result. 

It  is  proposed  to  use  this  method  of  determining  the 
relative  effective  diameter  of  the  pores  in  testing  brick  that 
are  to  be  placed  in  situations  where  drainage  is  the  domi- 
nant factor.  In  using  it,  the  method  of  procedure  will  be 
as  follows: 


38  HARDNESS   OF   BRICK  AND   THEIR   RESISTANCE  TO   FROST. 


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HARDNESS   OF  BRICK  AND   THEIR   RESISTANCE   TO    FROST.  39 

(1)  Dry  the  brick  forty-eight  hours  at  a  temperature 
of  300  degrees  Fahrenheit. 

(2)  Weigh,  after  cooling  to  room  temperature. 

(3)  By  room  temperature  is  meant  about  75  degrees 
Fahrenheit. 

(4)  Place  the  brick  on  edge  in  water  whose  final 
depth  after  the  brick  are  placed  is  one  inch. 

(5)  The  temperature  of  the  water  is  important,  as 
its  viscosity  changes  rapidly  with  temperature,  thus  chang- 
ing the  rate  of  flow.  If  it  is  kept  at  room  temperature,  or 
near  75° F  in  every  test,  the  results  may  be  safely  com- 
pared.    Otherwise  a  variable  factor  is  introduced. 

(6)  At  the  end  of  fifteen  minutes,  remove  the  brick 
and  weigh,  after  removing  the  surplus  water  clinging  to 
the  surface. 

(7)  Replace  in  water  for  forty-eight  hours. 

(8)  Weigh  as  before. 

(9)  The  percentage  of  water  absorbed  in  fifteen  min- 
utes, using  the  amount  absorbed  in  forty-eight  hours  as 
100  percent,  indicates  the  relative  rate  of  absorption. 
Methods  of  freezing. 

In  testing  brick  to  be  placed  in  a  position  where  they 
cannot  drain,  as  in  a  foundation,  they  should  be  saturated 
as  completely  as  possible  by  boiling,  or  under  the  air  pump, 
and  frozen  while  standing  in  water.  This  will  test  them 
under  conditions  that  are  similar  to  those  actually  occur- 
ring. The  brick  to  be  placed  in  situations  where  they  can 
drain,  as  in  the  upper  wall,  should  be  filled  with  w^ater  by 
soaking  and  placed  in  a  dry  can  w^hile  freezing.  These  are 
approximately  the  conditions  under  which  they  will  be 
placed  in  the  wall. 

At  the  temperatures  just  below  freezing,  overcooling 
plays  a  more  or  less  important  part.  In  tests  using  these 
temperatures,  the  results  are  uncertain  to  the  extent  of  the 
unknown  value  of  this  factor.  As  is  indicated  by  the  win- 
ter temperature  conditions  prevailing  in  Springfield  and 
Chicago,  the  drop  in  temperature  after  a  storm  is  probably 
to  about  ten  degrees  F.    It  is  probable  that  only  the  pores 


40  HARDNESS   OF   BRICK   AND   THEIR  RESISTANCE   TO   FROST. 

are  able  to  cool  to  this  temperature  without  freezing.  The 
additional  damage  resulting  from  freezing  them  is  at  most 
ver}^  slight,  and  the  differential  expansion  of  the  brick  it- 
self is  negligible.  Cooling  to  a  moderate  extent  below  this 
temperature  would  not  materially  alter  the  results.  It 
seems  to  the  writer,  therefore,  that  the  temperature  of  the 
freezing  can  should  be  at  least  as  low  as  that  prevailing  in 
nature,  and  that  average  temperatures  as  low  as  zero  F  are 
permissible.  It  is  best  for  the  comparison  of  results  to 
keep  between  the  limits  given.  As  it  is  impossible  to  con- 
trol the  temperature  of  the  atmosphere,  or  to  obtain  uni- 
formly low  temperatures  during  the  length  of  time  neces- 
sary— twenty  days — to  conduct  a  freezing  test,  a  refriger- 
ating plant  is  a  necessity. 

EXPERIMENTAL  DATA. 

As  an  illustration,  three  series  of  brick  were  selected, 
a  soft  mud  made  from  surface  clay,  a  soft  mud  made  from 
a  shale,  and  a  wire  cut  made  from  the  same  shale.  An  at- 
tempt was  made  in  selecting  the  brick  to  have  in  each  sSr- 
ies  four  grades  of  hardness  which  were  designated  as  soft, 
medium  soft,  medium  hard,  and  hard.  Each  grade  of  the 
surface  clay  was  represented  by  five  brick,  and  each  grade 
of  the  shale  brick  by  eight.  These  were  selected  by  eye  and 
by  the  sound  emitted  when  struck,  from  the  different  parts 
of  the  kilns,  each  series  coming  from  one  kiln,  and  were  as 
nearly  uniform  as  was  possible  to  obtain  under  the  circum- 
stances.   The  selections  were  made  by  Mr.  Purdy. 

Four  brick  of  each  grade  and  series  were  used  in  the 
tests  of  absorption  and  freezing.  The  brick  were  dried 
forty-eight  hours  in  an  air  bath  at  a  temperature  of  340 
degrees  F  and  weighed,  after  cooling  in  the  bath  to  room 
temperature.  They  were  then  placed  in  water  three  inches 
deep,  and  allowed  to  remain  forty-eight  hours,  after  which 
they  were  packed,  and  covered  in  a  can  placed  in  brine  to 
a  depth  that  brought  the  surface  of  the  brine  considerably 
above  the  top  level  of  the  brick.  The  brick  were  left  here 
from  ten  to  twenty-four  hours  until  they  were  thoroughly 


HARDNESS   OF    BRICK  AND  THEIR  RESISTANCE   TO   FROST.  41 

frozen.  They  were  then  removed  and  immersed  in  water 
at  a  temperature  of  approximateh'  tifty  degrees  F,  until 
they  were  completely  thawed  out.  This  cycle  of  freezing 
and  thawing  was  repeated  twenty  times.  After  the  final 
thawing,  the  brick  were  dried  as  before,  weighed  and  the 
loss  due  to  freezing  determined.  The  temperature  of  the 
brine  averaged  two  degrees  F  during  the  tests,  with  a  max- 
imum range  from  18  to  24  degrees.  As  all  brick  of  a  series 
were  frozen  together,  this  extreme  variation  did  not  affect 
the  comparison  of  the  results. 

The  brick  were  then  crushed,  together  with  unfrozen 
duplicates,  in  an  Olsen  testing  machine  of  200,000  pounds 
capacity.  For  the  crushing  test,  the  brick  were  first 
broken  with  a  hammer  and  the  half-brick  used,  in  order  to 
bring  them  within  the  capacity  of  the  machine.  Where 
there  was  but  one  brick  to  crush,  as  in  the  case  of  the 
unfrozen  ones  made  from  surface  clay,  both  halves  were 
crushed  and  the  average  taken.  The  brick  were  bedded  in 
plaster  of  paris  and  the  plaster  allowed  to  set  under  an  ini- 
tial pressure  of  2000  pounds.  It  was  impossible  to  get  the 
brick  bedded  uniformly  even  by  this  method,  and  there  was 
an  extreme  variation  of  400  pounds  in  halves  of  the  same 
brick.  The  brick  generally  failed  quietly,  although  occa- 
sionally, especially  among  the  harder  ones,  they  would  ex- 
plode and  send  fragments  flying  ten  feet  from  the  machine. 

As  the  number  of  the  unfrozen  bricks  varied,  the  num- 
ber tested  is  given  in  the  results.  The  results  given  by  the 
frozen  brick  are  invariably  the  average  of  four  specimens. 
As  it  was  practically  impossible  to  select  specimens  in  each 
grade  that  would  have  the  same  crushing  strength,  and 
since  the  perfection  of  bedding  necessarily  varied  in  the 
different  brick,  the  extreme  variation  in  each  grade  ranged 
from  400  pounds  in  the  softer  grades  to  4000  pounds  in  the 
harder  brick.  Otherwise  the  tests  are  quite  satisfactory, 
and  it  is  believed  as  nearly  accurate  as  was  possible  to  ob- 
tain under  the  circumstances. 


42 


HARDNESS   OF   BRICK  AND  THEIR   RESISTANCE   TO   FROST. 


Results  of  the  Freezing  Tests. 


Percent 

Percent 

Kind  of 

Grade  of 

Crushin 

5  Strength 

No. 

Loss 

Percent 

Ab- 

Brick 

Hardness 

Tested 

in 
Strength 

Pore 
Space 

sorption 

in  15 
minutes 

Remarks 

Frozen 

Unfrozen 

Soft 

Soft 

1194 

1374 

1 

13.1 

33.0 

83.0 

Frozen 

Mud 

Med.  soft 

3567 

3400 

1 

*4.6 

26.9 

93  4 

Brick 

Surface ' 

' '   hard 

4289 

5315 

1 

19.9 

21  2 

92.1 

Scaled 

Clay 

Hard  .  J,, 

7377 

7260 

1 

*1.6 

10.2 

25.1 

on  Face 

Soft 

Soft 

2671 

2913 

3 

8  6 

26  2 

52.9 

One  Brick 

Mud 

Med.  soft 

46  .'5 

6793 

3 

20.2 

17.8 

54.2 

Broken  in 

Shale 

"   liard 

8522 

10143 

2 

16.5 

11.6 

13  4 

Freezing 

Hard 
Soft 

7606 

11470 

4 

33  8 

5.8 

9.6 

Wire 

3729 

4637 

4 

19  6 

27.6 

40.0 

Two  bricks 

Cut 

Med.  soft 

6965 

8117 

4 

14.2 

17.1 

33  9 

freezing. 

Shale 

"   hard 

9165 

11315 

4 

19.4 

2  1 

34.5 

Two  bricks 

Hard 

115  . 

11997 

4 

4.1 

0.9 

47.3 

cracked  in 
freezing. 

*Gain. 

The  loss  in  weight  due  to  freezing  was  very  small, 
being  but  a  few  grams,  in  most  cases,  and  2%  in  an  excep- 
tional one. 

If  these  results  are  arranged  in  the  order  of  their 
pore-space,  hardness,  and  rate  of  absorption  as  indicated 
by  the  percentage  absorbed  in  the  first  fifteen  minutes,  the 
relations  of  these  factors  to  loss  of  strength  due  to  freezing 
is  clearing  brought  out. 


Arranged  in  the  order  of  hardness. 


Grade 

Surface  Clay 

Soft  Mud  Shale 

Wirecut  Shale 

Average  of  All 

Soft 

Med.  soft 
Med.  hard 
Hard 

13.1% 
4.6* 

19.9 
1.6* 

8.6% 
20.2 
16  6 
33  8 

19.6% 
14.2 

19  4 
4,1 

13.8% 
9.9 
18.6 
12  1 

*Gain. 

As  may  be  seen,  there  is  little  relation  between  the 
hardness  of  the  brick  and  its  resistance  to  frost.  The  sur- 
face clay  suffered  greatest  loss  when  burned  medium  hard, 
and  their  hard  burned  representatives  suffered  much  less; 


HARDNESS   OF   BRICK  AND   THEIR  RESISTANCE   TO    FROST. 


4S 


the  soft  mud  shale  suffered  most  when  hard  burned,  and 
the  softest  brick  the  least;  while  with  the  wire  cut  shale 
brick,  the  soft  and  medium  hard  suffered  most,  and  the 
hard  burned  much  less.  Upon  plotting  the  average  of  the 
three  kinds,  the  curve  zigzags  very  decidedly,  indicating 
that  hardness  in  itself  does  not  determine  the  amount  of 
resistance  the  brick  will  offer  to  frost.     (See  figure  3.) 

Arranged  as  to  Porespace. 


Porespace 

Per  cent.  Loss. 

Average  of  Similar  Groups. 

Porespace 

Per  cent.  Loss. 

33.0% 

13.1% 

33.0% 
27.0 

13.1% 

27.6 
26.9 
26.2 

19.6 
4.0* 

8.6 

7  9 

21.2 
17.8 
17.1 

11.6 
10.2 

19.9 
20  2 
14.2 

16  5 

1.6* 

18  0 
11  0 

18  1 

7.4 

5.8 
2  1 
0.9 

33.8 

19  4 

4  1 

3.0 

19  1 

*Gain 


Arranged  as  to  pore-space  even  greater  discrepancy 
than  in  the  former  case  is  seen.  The  plotted  curves  zigzag 
in  every  instance.  (See  figure  No.  4.)  They  should  be 
continuous,  if  there  were  any  relation  between  the  amount 
of  pore-space  and  resistance  to  frost.  An  interesting  series 
of  results  along  this  same  line  is  contained  in  Dr.  Buck- 
ley's report  on  the  building  stones  of  Missouri-^,  in  which 
the  same  lack  of  definite  relation  of  amount  of  pore  space 
and  resistance  to  frost  is  strikinglv  brought  out. 


21  Buckley,  Quarrying  Industry  of  Missouri,  2nd  ser.  Mo.  Geol.  Surv., 
Vol.  2,  PI.  LIX. 


44  HARDNESS   OF   BRICK  AND   THEIR   RESISTANCE   TO   FROST. 


TR,ANS.AM.CER.SOC.VOL.IX  JONES,  PLATE  III 

30 


Soft  M.Soft  M.Hard        Hard 

Relation    of  hardness  and 
percent  of  loss 


HARDNESS  OF   BRICK  AND  THEIR   RESISTANCE  TO    FROST.  46 


TRANS.AM.CER.SOC.VOL.IX         JONES,  PLATE  !V 

30r 


40  30  20  lO  0 

PERCENTAGE      PORE  SPACE 

RELATION     OF     PORE  5P/VCE     AND 

PERCENT  OF    LOS5 


46  HARDNESS  OF   BRICK   AND  THEIR   RESISTANCE   TO  FROST. 


Arranged  in  the  order  of  their  rates  of  absorption. 


Percent  absorbed  in 
15  minutes. 

Per  cent.  Loss 

Average   of  Similar   Groups. 

Per  cent.   Absorbed 

Per  cent  Loss 

93  4 
92.1 

83  0 

4.6* 
19  9 
13.1 

89  5 

9.4 

54.2 
52  9 
47  3 

20.2 
8.6 
4.1 

50.0 

11   0 

40  0 
34  6 
33  9 

19.6 
19.4 
14.2 

35.0 

17  7 

26  1 

1.6* 

^25.1 

1.6* 

13.4 
9  6 

,.    16  5 
33.8 

10.0 

25.1 

*Gain. 


When  the  brick  are  arranged  in  the  order  of  their  rates 
of  absorption,  as  indicated  by  the  amount  absorbed  in  the 
first  fifteen  minutes,  the  individual  curves  show  only  slight 
agreement  with  the  loss  caused  by  freezing.  (See  figure 
No.  5.)  The  surface  clay  seems  to  indicate  the  reverse  of 
the  theory  developed.  The  brick  that  absorbed  most  slowly, 
and  therefore  had  the  smallest  pores,  suffered  least.  The 
explanation  of  this  probably  lies  in  the  number  of  unfrozen 
bricly  tested.  Only  one  in  each  grade  was  available,  and 
consequently  the  individual  variations  in  strength,  perfec- 
tion of  bedding  in  the  machine,  and  other  conditions,  the 
effect  of  which  it  is  impossible  to  avoid  except  by  using  a 
number  of  test  pieces,  are  prominent.  Indeed,  two  of  the 
grades  indicate  a  gain  in  strength  rather  than  a  loss  due 
to  freezing,  which  is  not  a  reasonable  thing  to  believe  and, 
consequently,  while  the  evidence  of  the  surface  clay  brick 
is  accepted,  not  as  much  weight  can  be  given  it  as  that  of 
the  shale  brick  which  were  tested  more  completely.    With 


HARDNESS  OF   BRICK   AND  THEIR  RESISTANCE  TO    FROST.  47 


30 

TRANS.AM  CER.SOC  VOL.  l> 

JONES, 

PLATE    V 

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1 

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1 

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1 

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\00       90        &0      70         eO      50        '^O        50        2.0        \o         o 
PERCENTAGE    ABSORPTION     IN     l5    MINUTES 

RELATION    OF    WATER  ABSORBED    IN   15    MINUTES 
A.NO    PERCENT     OF  LOSS 


48  HARDNESS   OF   BRICK   AND  THEIR   RESISTANCE  TO    FROST. 

the  latter,  the  finer-pored  brick,  even  though  they  were  not 
always  the  hardest  or  possessed  the  greatest  pore-space, 
generally  suffered  the  greatest  loss.  Upon  averaging  the 
groups  with  approximately  the  same  rate  of  absorption,  a 
curve  is  obtained  that  is  continuous  from  beginning  to  end. 
The  only  exception  is  one  of  the  questionable  values  of  the 
surface  clay  brick.  As  the  individual  variations  can  only 
be  eliminated  by  the  use  of  a  considerable  number  of  speci- 
mens, it  is  believed  that  this  curve  approximates  the  truth, 
and  indicates  the  value  of  the  rate  of  absorption  as  an  in- 
dication of  the  power  of  brick  to  withstand  the  ravages  of 
frost.  This  is  true,  since  the  rate  of  absorption  is  governed 
by  the  same  factor  that  controls  the  rate  of  flow  through 
the  pores,  and  consequent  relief  from  danger  of  damage  by 
frost.  Therefore  the  results  obtained  from  the  brick  tested 
are  believed  to  confirm  the  theory  developed. 

SUMMARY  AND  CONCLUSION. 

It  has  been  shown  that  the  pores  in  brick  originate  in 
the  spaces  between  the  grains  of  clay  used  in  manufacture. 
The  size  of  the  pores  depends  upon  the  size  of  the  grains, 
and  upon  the  manner  in  w^hich  they  are  packed.  The 
coarser  pores  result  from  the  larger  sized  grains  and  looser 
packing.  Scattered  through  the  brick  are  numerous  cracks 
and  cavities,  known  as  laminations,  which  are  produced  in 
several  ways  during  the  process  of  manufacture.  These 
are  relatively  much  larger  than  the  pores.*  As  they  are  not 
in  direct  contact,  their  only  connection  with  each  other, 
and  the  surface  of  the  brick  is  through  the  pores.  The 
pores  and  the  laminations  together  make  up  the  pore-space 
of  the  brick,  the  laminations  furnishing  the  major  part. 

Tlie  method  of  -manufacture  determines  the  compact- 
ness with  which  the  grains  are  packed,  and  therefore  the 
size  of  the  pores  and  the  pore-space.  Other  things  being 
equal,  the  soft  mud  process  will  make  a  more  porous  brick 
than  the  stiff  mud  process,  on  account  of  the  greater 
amount  of  water  and  slighter  pressure  used. 

During  the  water-smoking  and  oxidation  period  of  the 


HARDNESS  OF   BRICK  AND   THEIR  RESISTANCE   TO    FROST.  49 

burn,  pores  are  opened  and  enlarged  bv  the  escaping  gases. 
The  bricks  have  tlieir  maximum  amount  of  pore-space  at 
this  time,  and  it  remains  at  this  value  until  the  amorphous 
material  begins  to  melt.  When  this  happens,  the  grains 
soften  around  their  borders  and  run  together.  This  tends 
to  obstruct  the  pores,  and  eventually  completely  closes 
them  at  different  points  along  their  length.  The  parts  of 
the  pores  that  are  enclosed  between  the  points  sealed,  con- 
tain gas  that  prevents  the  further  closure  of  the  pore.  As 
the  amount  of  glass  increases,  the  enclosed  gases  form 
bubbles  which  become  spherical  in  shape.  These  bubbles 
are  completely  shut  off  from  the  system  of  pores,  and  the 
pore-space  apparently  decreases.  Those  pores  that  are  not 
sealed  are  obstructed,  which  is  equivalent  to  making  them 
smaller. 

The  strength  of  the  brick  increases  as  it  is  burned,  and 
also  its  rigidity  or  brittleness.  This  gives  the  brick  greater 
resistance  to  strain,  l)ut  decreases  the  distance  it  may  be 
deformed  without  breaking.  A  given  amount  of  expansion 
or  contraction  may,  therefore,  rupture  a  rigid  brick,  when 
it  would  not  harm  a  tougher  one. 

Owing  to  the  universal  occurrence  and  abundance  of 
water,  and  its  property  of  expanding  upon  freezing,  it  is 
the  only  substance  that  under  ordinary  conditions  causes 
any  considerable  damage  to  brick.  It  expands  one-tenth  of 
its  volume  when  freezing,  and  when  it  is  confined  within 
the  brick,  may  burst  it  upon  freezing.  The  important 
factor  serving  to  mitigate  the  destructive  effect  of  freezing- 
water  is  the  opportunity  generally  afforded  for  a  portion 
of  the  water  to  drain,  before  the  brick  cools  sufficiently  to 
freeze.  The  temperature  at  which  the  brick  freezes  may  be 
blow  the  ordinary  freezing  point  of  water,  owing  to  the 
property  of  capillary  tubes  which  delays  the  freezing  of 
water  within  them  until  a  lower  temperature  is  reached.  It 
is  not  probable  that  freezing  in  the  larger  openings  is  en- 
tirely prevented  at  the  temperatures  prevalent  during  the 
winter  months  in  our  northern  States. 

The  amount  of  water  that  may  drain  depends  upon  the 
rate  with  which  it  passes  through  the  pores.    This  is  deter- 


50  HARDNESS   OP  BRICK   AND   THEIR  RESISTANCE  TO   FROST. 

mined  by  the  size  of  the  pores,  and  is  much  greater  in 
coarse  pores  than  in  the  finer  ones.  It  was  found  that 
water  will  pass  through  pores  four  times  as  fast  if  they 
are  doubled  in  size,  and  nine  times  as  fast  if  they  are 
trebled.  Although  the  lamination  cracks  contain  the  bulk 
of  the  water,  they  are  dependent  upon  the  pores  for  drain- 
age. Consequently  the  amount  of  damage  done  in  a  brick 
depends  on  the  size  of  its  pores,  since  this  governs  the  rap- 
idity with  which  it  will  drain. 

In  the  foundation  at  the  water  line,  the  brick  are  con- 
tinually in  contact  with  water.  As  any  air  originally  con- 
fined in  them  will  eventually  diffuse,  they  become  com- 
pletely saturated.  The  brick  just  above  the  water  line  are 
filled  through  capillary  action  from  below,  and  from  the 
drainage  of  the  upper  wall.  These, also  become  completely 
saturated,  and  as  the  frost  seldom  reaches  the  water  line, 
it  is  this  part  of  the  wall  that  suffers  most.  The  amount 
of  damage  done  the  brick  in  this  zone  of  saturation  is  pro- 
portional to  the  total  pore-space,  and  the  strength  of  the 
brick.  The  best  brick  for  this  situation  is,  therefore,  the 
one  that  is  strongest  and  least  porous. 

In  the  upper  Avail  the  brick  are  able  to  drain.  The 
amount  of  damage  is  therefore  proportional  to  the  rate  of 
flow  through  the  pores,  and  the  total  amoutn  of  pore-space 
has  little  direct  effect.  As  in  freezing,  tests  giving  similar 
effects  are  present,  it  is  easy  to  understand  why  the  hard- 
burned,  fine-pored  brick  suffered  more  than  those  softer, 
but  with  coarser  pores. 

It  is  of  vital  importance  to  consider  the  future  position 
and  conditions  in  which  brick  are  to  be  placed,  in  making 
tests  to  determine  the  ones  best  adapted.  In  the  situations 
where  saturation  is  the  controlling  condition,  as  in  foun- 
dations, evidently  the  brick  that  contains  the  least  amount 
of  pore-space  is  the  best.  In  consequence  it  is  necessary  to 
determine  the  total  pore-space,  minute  pores  and  all,  since 
these  become  filled,  sooner  or  later,  in  saturated  situations. 
This  cannot  be  done  by  the  method  of  soaking  at  present 
used,  but  may  be  approximated  by  boiling  or  the  use  of 
the  air  pump. 


t 


HARDNESS   OK    IIHU'K   AN1>   THKIH    KKSISTANOK   TO    KROST.  ■)1 

In  situations  where  drainage  is  the  controlling  factor 
the  brick  that  will  drain  fastest  is  the  best,  if  injury  from 
frost  only  is  considered.  The  relative  rate  with  which  the 
brick  will  drain  must  be  obtained.  This  may  be  easily  done 
by  the  method  proposed  on  page  IV,K 

The  crushing  strength  of  brick  has  an  important  value 
in  foundation  brick,  as  it  indicates  the  relative  resistance 
the  brick  will  offer  to  expansion  of  the  freezing  water.  The 
brick  in  the  upper  wall,  on  the  other  hand,  need  only  the 
strength  necessary  to  carry  their  load. 

Consequently  these  three  tests, — total  pore-space,  rate 
of  flow  through  the  pores,  and  crushing  strength,— should 
give  a  correct  indication  of  the  power  of  a  brick  to  with- 
stand frost.  In  the  brick  to  be  used  in  situations  of  satur- 
ation, only  pore-space  and  strength  need  be  determined. 

The  characters  of  the  brick  which  are  altered  during 
burning  are:  the  size  of  the  pores,  the  amount  of  pore- 
space,  the  strength  of  the  brick,  and  its  rigidity.  The 
harder  burned  brick  have  finer  pores,  a  smaller  amount  of 
pore-space,  greater  strength,  and  greater  rigidity.  They 
therefore  drain  more  slowly,  contain  a  smaller  amount  of 
water  when  jftlled,  have  greater  strength  to  resist  the  ex- 
pansion of  freezing  water,  but  will  rupture  with  a  smaller 
amount  of  expansion.  Whether  or  not  the  hardest  burned 
brick  will  resist  frost  best,  depends  upon  the  relation  be- 
tween its  gain  in  strength  and  loss  of  pore-space  on  the 
one  hand,  and  the  decrease  in  the  effective  diameter  of  its 
pores  and  increase  in  brittleness  on  the  other.  If  the  for- 
mer factors  are  progressively  altered  more  rapidly  during 
the  burn  than  the  latter,  the  harder  burned  brick  will  be 
the  more  durable.  If,  on  the  other  hand,  the  latter  factors 
are  the  ones  to  develop  more  rapidly,  the  power  of  resist- 
ance of  the  brick  as  the  burn  progresses  is  relatively  de- 
creasing. The  quantitative  expression  of  this  relation  has 
not  been  worked  out,  and  must  be  left  for  some  future  in- 
vestigator. The  present  investigation,  however,  has  shown 
the  direction  in  which  the  relation  between  hardness  and 
resistance  to  frost  mav  be  found. 


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